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C++ Mathematical Expression Library
Home Page: http://www.partow.net/programming/exprtk/index.html
exprtk's Introduction
C++ Mathematical Expression Toolkit Library
[00 - INTRODUCTION]
The C++ Mathematical Expression Toolkit Library (ExprTk) is a simple
to use, easy to integrate and extremely efficient run-time
mathematical expression parsing and evaluation engine. The parsing
engine supports numerous forms of functional and logic processing
semantics and is easily extendible.
[01 - CAPABILITIES]
The ExprTk expression evaluator supports the following fundamental
arithmetic operations, functions and processes:
(00) Types: Scalar, Vector, String
(01) Basic operators: +, -, *, /, %, ^
(02) Assignment: :=, +=, -=, *=, /=, %=
(03) Equalities &
Inequalities: =, ==, <>, !=, <, <=, >, >=
(04) Boolean logic: and, mand, mor, nand, nor, not, or, shl, shr,
xnor, xor, true, false
(05) Functions: abs, avg, ceil, clamp, equal, erf, erfc, exp,
expm1, floor, frac, log, log10, log1p, log2,
logn, max, min, mul, ncdf, nequal, root,
round, roundn, sgn, sqrt, sum, swap, trunc
(06) Trigonometry: acos, acosh, asin, asinh, atan, atanh, atan2,
cos, cosh, cot, csc, sec, sin, sinc, sinh,
tan, tanh, hypot, rad2deg, deg2grad, deg2rad,
grad2deg
(07) Control
structures: if-then-else, ternary conditional, switch-case,
return-statement
(08) Loop statements: while, for, repeat-until, break, continue
(09) String
processing: in, like, ilike, concatenation
(10) Optimisations: constant-folding, simple strength reduction and
dead code elimination
(11) Calculus: numerical integration and differentiation
[02 - EXAMPLE EXPRESSIONS]
The following is a short listing of the types of mathematical
expressions that can be parsed and evaluated using the ExprTk library.
(01) sqrt(1 - (3 / x^2))
(02) clamp(-1, sin(2 * pi * x) + cos(y / 2 * pi), +1)
(03) sin(2.34e-3 * x)
(04) if(((x[2] + 2) == 3) and ((y + 5) <= 9),1 + w, 2 / z)
(05) inrange(-2,m,+2) == if(({-2 <= m} and [m <= +2]),1,0)
(06) ({1/1}*[1/2]+(1/3))-{1/4}^[1/5]+(1/6)-({1/7}+[1/8]*(1/9))
(07) a * exp(2.2 / 3.3 * t) + c
(08) z := x + sin(2.567 * pi / y)
(09) u := 2.123 * {pi * z} / (w := x + cos(y / pi))
(10) 2x + 3y + 4z + 5w == 2 * x + 3 * y + 4 * z + 5 * w
(11) 3(x + y) / 2.9 + 1.234e+12 == 3 * (x + y) / 2.9 + 1.234e+12
(12) (x + y)3.3 + 1 / 4.5 == [x + y] * 3.3 + 1 / 4.5
(13) (x + y[i])z + 1.1 / 2.7 == (x + y[i]) * z + 1.1 / 2.7
(14) (sin(x / pi) cos(2y) + 1) == (sin(x / pi) * cos(2 * y) + 1)
(15) 75x^17 + 25.1x^5 - 35x^4 - 15.2x^3 + 40x^2 - 15.3x + 1
(16) (avg(x,y) <= x + y ? x - y : x * y) + 2.345 * pi / x
(17) while (x <= 100) { x -= 1; }
(18) x <= 'abc123' and (y in 'AString') or ('1x2y3z' != z)
(19) ((x + 'abc') like '*123*') or ('a123b' ilike y)
(20) sgn(+1.2^3.4z / -5.6y) <= {-7.8^9 / -10.11x }
[03 - COPYRIGHT NOTICE]
Free use of the C++ Mathematical Expression Toolkit Library is
permitted under the guidelines and in accordance with the most current
version of the Common Public License.
http://www.opensource.org/licenses/cpl1.0.php
[04 - DOWNLOADS & UPDATES]
The most recent version of the C++ Mathematical Expression Toolkit
Library including all updates and tests can be found at the following
locations:
(a) Download: http://www.partow.net/programming/exprtk/index.html
(b) Repository: https://github.com/ArashPartow/exprtk
[05 - INSTALLATION]
The header file exprtk.hpp should be placed in a project or system
include path (e.g: /usr/include/).
[06 - COMPILATION]
(a) For a complete build: make clean all
(b) For a PGO build: make clean pgo
(c) To strip executables: make strip_bin
(d) Execute valgrind check: make valgrind_check
[07 - COMPILER COMPATIBILITY]
ExprTk has been built error and warning free using the following set
of C++ compilers:
(*) GNU Compiler Collection (3.3+)
(*) Intel C++ Compiler (8.x+)
(*) Clang/LLVM (1.1+)
(*) PGI C++ (10.x+)
(*) Microsoft Visual Studio C++ Compiler (8.1+)
(*) Comeau C++ Compiler (4.3+)
(*) IBM XL C/C++ (9.x+)
(*) C++ Builder (XE4+)
[08 - BUILT-IN OPERATIONS & FUNCTIONS]
(0) Arithmetic & Assignment Operators
+----------+---------------------------------------------------------+
| OPERATOR | DEFINITION |
+----------+---------------------------------------------------------+
| + | Addition between x and y. (eg: x + y) |
+----------+---------------------------------------------------------+
| - | Subtraction between x and y. (eg: x - y) |
+----------+---------------------------------------------------------+
| * | Multiplication between x and y. (eg: x * y) |
+----------+---------------------------------------------------------+
| / | Division between x and y. (eg: x / y) |
+----------+---------------------------------------------------------+
| % | Modulus of x with respect to y. (eg: x % y) |
+----------+---------------------------------------------------------+
| ^ | x to the power of y. (eg: x ^ y) |
+----------+---------------------------------------------------------+
| := | Assign the value of x to y. Where y is either a variable|
| | or vector type. (eg: y := x) |
+----------+---------------------------------------------------------+
| += | Increment x by the value of the expression on the right |
| | hand side. Where x is either a variable or vector type. |
| | (eg: x += abs(y - z)) |
+----------+---------------------------------------------------------+
| -= | Decrement x by the value of the expression on the right |
| | hand side. Where x is either a variable or vector type. |
| | (eg: x[i] -= abs(y + z)) |
+----------+---------------------------------------------------------+
| *= | Assign the multiplication of x by the value of the |
| | expression on the righthand side to x. Where x is either|
| | a variable or vector type. |
| | (eg: x *= abs(y / z)) |
+----------+---------------------------------------------------------+
| /= | Assign the division of x by the value of the expression |
| | on the right-hand side to x. Where x is either a |
| | variable or vector type. (eg: x[i + j] /= abs(y * z)) |
+----------+---------------------------------------------------------+
| %= | Assign x modulo the value of the expression on the right|
| | hand side to x. Where x is either a variable or vector |
| | type. (eg: x[2] %= y ^ 2) |
+----------+---------------------------------------------------------+
(1) Equalities & Inequalities
+----------+---------------------------------------------------------+
| OPERATOR | DEFINITION |
+----------+---------------------------------------------------------+
| == or = | True only if x is strictly equal to y. (eg: x == y) |
+----------+---------------------------------------------------------+
| <> or != | True only if x does not equal y. (eg: x <> y or x != y) |
+----------+---------------------------------------------------------+
| < | True only if x is less than y. (eg: x < y) |
+----------+---------------------------------------------------------+
| <= | True only if x is less than or equal to y. (eg: x <= y) |
+----------+---------------------------------------------------------+
| > | True only if x is greater than y. (eg: x > y) |
+----------+---------------------------------------------------------+
| >= | True only if x greater than or equal to y. (eg: x >= y) |
+----------+---------------------------------------------------------+
(2) Boolean Operations
+----------+---------------------------------------------------------+
| OPERATOR | DEFINITION |
+----------+---------------------------------------------------------+
| true | True state or any value other than zero (typically 1). |
+----------+---------------------------------------------------------+
| false | False state, value of zero. |
+----------+---------------------------------------------------------+
| and | Logical AND, True only if x and y are both true. |
| | (eg: x and y) |
+----------+---------------------------------------------------------+
| mand | Multi-input logical AND, True only if all inputs are |
| | true. Left to right short-circuiting of expressions. |
| | (eg: mand(x > y, z < w, u or v, w and x)) |
+----------+---------------------------------------------------------+
| mor | Multi-input logical OR, True if at least one of the |
| | inputs are true. Left to right short-circuiting of |
| | expressions. (eg: mor(x > y, z < w, u or v, w and x)) |
+----------+---------------------------------------------------------+
| nand | Logical NAND, True only if either x or y is false. |
| | (eg: x nand y) |
+----------+---------------------------------------------------------+
| nor | Logical NOR, True only if the result of x or y is false |
| | (eg: x nor y) |
+----------+---------------------------------------------------------+
| not | Logical NOT, Negate the logical sense of the input. |
| | (eg: not(x and y) == x nand y) |
+----------+---------------------------------------------------------+
| or | Logical OR, True if either x or y is true. (eg: x or y) |
+----------+---------------------------------------------------------+
| xor | Logical XOR, True only if the logical states of x and y |
| | differ. (eg: x xor y) |
+----------+---------------------------------------------------------+
| xnor | Logical XNOR, True iff the biconditional of x and y is |
| | satisfied. (eg: x xnor y) |
+----------+---------------------------------------------------------+
| & | Similar to AND but with left to right expression short |
| | circuiting optimisation. (eg: (x & y) == (y and x)) |
+----------+---------------------------------------------------------+
| | | Similar to OR but with left to right expression short |
| | circuiting optimisation. (eg: (x | y) == (y or x)) |
+----------+---------------------------------------------------------+
(3) General Purpose Functions
+----------+---------------------------------------------------------+
| FUNCTION | DEFINITION |
+----------+---------------------------------------------------------+
| abs | Absolute value of x. (eg: abs(x)) |
+----------+---------------------------------------------------------+
| avg | Average of all the inputs. |
| | (eg: avg(x,y,z,w,u,v) == (x + y + z + w + u + v) / 6) |
+----------+---------------------------------------------------------+
| ceil | Smallest integer that is greater than or equal to x. |
+----------+---------------------------------------------------------+
| clamp | Clamp x in range between r0 and r1, where r0 < r1. |
| | (eg: clamp(r0,x,r1) |
+----------+---------------------------------------------------------+
| equal | Equality test between x and y using normalized epsilon |
+----------+---------------------------------------------------------+
| erf | Error function of x. (eg: erf(x)) |
+----------+---------------------------------------------------------+
| erfc | Complimentary error function of x. (eg: erfc(x)) |
+----------+---------------------------------------------------------+
| exp | e to the power of x. (eg: exp(x)) |
+----------+---------------------------------------------------------+
| expm1 | e to the power of x minus 1, where x is very small. |
| | (eg: expm1(x)) |
+----------+---------------------------------------------------------+
| floor | Largest integer that is less than or equal to x. |
| | (eg: floor(x)) |
+----------+---------------------------------------------------------+
| frac | Fractional portion of x. (eg: frac(x)) |
+----------+---------------------------------------------------------+
| hypot | Hypotenuse of x and y (eg: hypot(x,y) = sqrt(x*x + y*y))|
+----------+---------------------------------------------------------+
| iclamp | Inverse-clamp x outside of the range r0 and r1. Where |
| | r0 < r1. If x is within the range it will snap to the |
| | closest bound. (eg: iclamp(r0,x,r1) |
+----------+---------------------------------------------------------+
| inrange | In-range returns 'true' when x is within the range r0 |
| | and r1. Where r0 < r1. (eg: inrange(r0,x,r1) |
+----------+---------------------------------------------------------+
| log | Natural logarithm of x. (eg: log(x)) |
+----------+---------------------------------------------------------+
| log10 | Base 10 logarithm of x. (eg: log10(x)) |
+----------+---------------------------------------------------------+
| log1p | Natural logarithm of 1 + x, where x is very small. |
| | (eg: log1p(x)) |
+----------+---------------------------------------------------------+
| log2 | Base 2 logarithm of x. (eg: log2(x)) |
+----------+---------------------------------------------------------+
| logn | Base N logarithm of x. where n is a positive integer. |
| | (eg: logn(x,8)) |
+----------+---------------------------------------------------------+
| max | Largest value of all the inputs. (eg: max(x,y,z,w,u,v)) |
+----------+---------------------------------------------------------+
| min | Smallest value of all the inputs. (eg: min(x,y,z,w,u)) |
+----------+---------------------------------------------------------+
| mul | Product of all the inputs. |
| | (eg: mul(x,y,z,w,u,v,t) == (x * y * z * w * u * v * t)) |
+----------+---------------------------------------------------------+
| ncdf | Normal cumulative distribution function. (eg: ncdf(x)) |
+----------+---------------------------------------------------------+
| nequal | Not-equal test between x and y using normalized epsilon |
+----------+---------------------------------------------------------+
| root | Nth-Root of x. where n is a positive integer. |
| | (eg: root(x,3)) |
+----------+---------------------------------------------------------+
| round | Round x to the nearest integer. (eg: round(x)) |
+----------+---------------------------------------------------------+
| roundn | Round x to n decimal places (eg: roundn(x,3)) |
| | where n > 0 and is an integer. |
| | (eg: roundn(1.2345678,4) == 1.2346) |
+----------+---------------------------------------------------------+
| sgn | Sign of x, -1 where x < 0, +1 where x > 0, else zero. |
| | (eg: sgn(x)) |
+----------+---------------------------------------------------------+
| sqrt | Square root of x, where x > 0. (eg: sqrt(x)) |
+----------+---------------------------------------------------------+
| sum | Sum of all the inputs. |
| | (eg: sum(x,y,z,w,u,v,t) == (x + y + z + w + u + v + t)) |
+----------+---------------------------------------------------------+
| swap | Swap the values of the variables x and y and return the |
| <=> | current value of y. (eg: swap(x,y) or x <=> y) |
+----------+---------------------------------------------------------+
| trunc | Integer portion of x. (eg: trunc(x)) |
+----------+---------------------------------------------------------+
(4) Trigonometry Functions
+----------+---------------------------------------------------------+
| FUNCTION | DEFINITION |
+----------+---------------------------------------------------------+
| acos | Arc cosine of x expressed in radians. Interval [-1,+1] |
| | (eg: acos(x)) |
+----------+---------------------------------------------------------+
| acosh | Inverse hyperbolic cosine of x expressed in radians. |
| | (eg: acosh(x)) |
+----------+---------------------------------------------------------+
| asin | Arc sine of x expressed in radians. Interval [-1,+1] |
| | (eg: asin(x)) |
+----------+---------------------------------------------------------+
| asinh | Inverse hyperbolic sine of x expressed in radians. |
| | (eg: asinh(x)) |
+----------+---------------------------------------------------------+
| atan | Arc tangent of x expressed in radians. Interval [-1,+1] |
| | (eg: atan(x)) |
+----------+---------------------------------------------------------+
| atan2 | Arc tangent of (x / y) expressed in radians. [-pi,+pi] |
| | eg: atan2(x,y) |
+----------+---------------------------------------------------------+
| atanh | Inverse hyperbolic tangent of x expressed in radians. |
| | (eg: atanh(x)) |
+----------+---------------------------------------------------------+
| cos | Cosine of x. (eg: cos(x)) |
+----------+---------------------------------------------------------+
| cosh | Hyperbolic cosine of x. (eg: cosh(x)) |
+----------+---------------------------------------------------------+
| cot | Cotangent of x. (eg: cot(x)) |
+----------+---------------------------------------------------------+
| csc | Cosecant of x. (eg: csc(x)) |
+----------+---------------------------------------------------------+
| sec | Secant of x. (eg: sec(x)) |
+----------+---------------------------------------------------------+
| sin | Sine of x. (eg: sin(x)) |
+----------+---------------------------------------------------------+
| sinc | Sine cardinal of x. (eg: sinc(x)) |
+----------+---------------------------------------------------------+
| sinh | Hyperbolic sine of x. (eg: sinh(x)) |
+----------+---------------------------------------------------------+
| tan | Tangent of x. (eg: tan(x)) |
+----------+---------------------------------------------------------+
| tanh | Hyperbolic tangent of x. (eg: tanh(x)) |
+----------+---------------------------------------------------------+
| deg2rad | Convert x from degrees to radians. (eg: deg2rad(x)) |
+----------+---------------------------------------------------------+
| deg2grad | Convert x from degrees to gradians. (eg: deg2grad(x)) |
+----------+---------------------------------------------------------+
| rad2deg | Convert x from radians to degrees. (eg: rad2deg(x)) |
+----------+---------------------------------------------------------+
| grad2deg | Convert x from gradians to degrees. (eg: grad2deg(x)) |
+----------+---------------------------------------------------------+
(5) String Processing
+----------+---------------------------------------------------------+
| FUNCTION | DEFINITION |
+----------+---------------------------------------------------------+
| = , == | All common equality/inequality operators are applicable |
| !=, <> | to strings and are applied in a case sensitive manner. |
| <=, >= | In the following example x, y and z are of type string. |
| < , > | (eg: not((x <= 'AbC') and ('1x2y3z' <> y)) or (z == x) |
+----------+---------------------------------------------------------+
| in | True only if x is a substring of y. |
| | (eg: x in y or 'abc' in 'abcdefgh') |
+----------+---------------------------------------------------------+
| like | True only if the string x matches the pattern y. |
| | Available wildcard characters are '*' and '?' denoting |
| | zero or more and zero or one matches respectively. |
| | (eg: x like y or 'abcdefgh' like 'a?d*h') |
+----------+---------------------------------------------------------+
| ilike | True only if the string x matches the pattern y in a |
| | case insensitive manner. Available wildcard characters |
| | are '*' and '?' denoting zero or more and zero or one |
| | matches respectively. |
| | (eg: x ilike y or 'a1B2c3D4e5F6g7H' ilike 'a?d*h') |
+----------+---------------------------------------------------------+
| [r0:r1] | The closed interval [r0,r1] of the specified string. |
| | eg: Given a string x with a value of 'abcdefgh' then: |
| | 1. x[1:4] == 'bcde' |
| | 2. x[ :5] == x[:5] == 'abcdef' |
| | 3. x[3: ] == x[3:] =='cdefgh' |
| | 4. x[ : ] == x[:] == 'abcdefgh' |
| | 5. x[4/2:3+2] == x[2:5] == 'cdef' |
| | |
| | Note: Both r0 and r1 are assumed to be integers, where |
| | r0 <= r1. They may also be the result of an expression, |
| | in the event they have fractional components truncation |
| | will be performed. (eg: 1.67 --> 1) |
+----------+---------------------------------------------------------+
| := | Assign the value of x to y. Where y is a mutable string |
| | or string range and x is either a string or a string |
| | range. eg: |
| | 1. y := x |
| | 2. y := 'abc' |
| | 3. y := x[:i + j] |
| | 4. y := '0123456789'[2:7] |
| | 5. y := '0123456789'[2i + 1:7] |
| | 6. y := (x := '0123456789'[2:7]) |
| | 7. y[i:j] := x |
| | 8. y[i:j] := (x + 'abcdefg'[8 / 4:5])[m:n] |
| | |
| | Note: For options 7 and 8 the shorter of the two ranges |
| | will denote the number characters that are to be copied.|
+----------+---------------------------------------------------------+
| + | Concatenation of x and y. Where x and y are strings or |
| | string ranges. eg |
| | 1. x + y |
| | 2. x + 'abc' |
| | 3. x + y[:i + j] |
| | 4. x[i:j] + y[2:3] + '0123456789'[2:7] |
| | 5. 'abc' + x + y |
| | 6. 'abc' + '1234567' |
| | 7. (x + 'a1B2c3D4' + y)[i:2j] |
+----------+---------------------------------------------------------+
| += | Append to x the value of y. Where x is a mutable string |
| | and y is either a string or a string range. eg: |
| | 1. x += y |
| | 2. x += 'abc' |
| | 3. x += y[:i + j] + 'abc' |
| | 4. x += '0123456789'[2:7] |
+----------+---------------------------------------------------------+
| <=> | Swap the values of x and y. Where x and y are mutable |
| | strings. (eg: x <=> y) |
+----------+---------------------------------------------------------+
| [] | The string size operator returns the size of the string |
| | being actioned. |
| | eg: |
| | 1. 'abc'[] == 3 |
| | 2. var max_str_length := max(s0[],s1[],s2[],s3[]) |
| | 3. ('abc' + 'xyz')[] == 6 |
| | 4. (('abc' + 'xyz')[1:4])[] == 4 |
+----------+---------------------------------------------------------+
(6) Control Structures
+----------+---------------------------------------------------------+
|STRUCTURE | DEFINITION |
+----------+---------------------------------------------------------+
| if | If x is true then return y else return z. |
| | eg: |
| | 1. if(x, y, z) |
| | 2. if((x + 1) > 2y, z + 1, w / v) |
| | 3. if(x > y) z; |
| | 4. if(x <= 2*y) { z + w }; |
+----------+---------------------------------------------------------+
| if-else | The if-else/else-if statement. Subject to the condition |
| | branch the statement will return either the value of the|
| | consequent or the alternative branch. |
| | eg: |
| | 1. if (x > y) z; else w; |
| | 2. if (x > y) z; else if (w != u) v; |
| | 3. if (x < y) {z; w + 1;} else u; |
| | 4. if ((x != y) and (z > w)) |
| | { |
| | y := sin(x) / u; |
| | z := w + 1; |
| | } |
| | else if (x > (z + 1)) |
| | { |
| | w := abs (x - y) + z; |
| | u := (x + 1) > 2y ? 2u : 3u; |
| | } |
+----------+---------------------------------------------------------+
| switch | The first true case condition that is encountered will |
| | determine the result of the switch. If none of the case |
| | conditions hold true, the default action is assumed as |
| | the final return value. This is sometimes also known as |
| | a multi-way branch mechanism. |
| | eg: |
| | switch |
| | { |
| | case x > (y + z) : 2 * x / abs(y - z); |
| | case x < 3 : sin(x + y); |
| | default : 1 + x; |
| | } |
+----------+---------------------------------------------------------+
| while | The structure will repeatedly evaluate the internal |
| | statement(s) 'while' the condition is true. The final |
| | statement in the final iteration will be used as the |
| | return value of the loop. |
| | eg: |
| | while ((x -= 1) > 0) |
| | { |
| | y := x + z; |
| | w := u + y; |
| | } |
+----------+---------------------------------------------------------+
| repeat/ | The structure will repeatedly evaluate the internal |
| until | statement(s) 'until' the condition is true. The final |
| | statement in the final iteration will be used as the |
| | return value of the loop. |
| | eg: |
| | repeat |
| | y := x + z; |
| | w := u + y; |
| | until ((x += 1) > 100) |
+----------+---------------------------------------------------------+
| for | The structure will repeatedly evaluate the internal |
| | statement(s) while the condition is true. On each loop |
| | iteration, an 'incrementing' expression is evaluated. |
| | The conditional is mandatory whereas the initialiser |
| | and incrementing expressions are optional. |
| | eg: |
| | for (var x := 0; (x < n) and (x != y); x += 1) |
| | { |
| | y := y + x / 2 - z; |
| | w := u + y; |
| | } |
+----------+---------------------------------------------------------+
| break | Break terminates the execution of the nearest enclosed |
| break[] | loop, allowing for the execution to continue on external|
| | to the loop. The default break statement will set the |
| | return value of the loop to NaN, where as the return |
| | based form will set the value to that of the break |
| | expression. |
| | eg: |
| | while ((i += 1) < 10) |
| | { |
| | if (i < 5) |
| | j -= i + 2; |
| | else if (i % 2 == 0) |
| | break; |
| | else |
| | break[2i + 3]; |
| | } |
+----------+---------------------------------------------------------+
| continue | Continue results in the remaining portion of the nearest|
| | enclosing loop body to be skipped. |
| | eg: |
| | for (var i := 0; i < 10; i += 1) |
| | { |
| | if (i < 5) |
| | continue; |
| | j -= i + 2; |
| | } |
+----------+---------------------------------------------------------+
| return | Return immediately from within the current expression. |
| | With the option of passing back a variable number of |
| | values (scalar, vector or string). eg: |
| | 1. return [1]; |
| | 2. return [x, 'abx']; |
| | 3. return [x, x + y,'abx']; |
| | 4. return []; |
| | 5. if (x < y) |
| | return [x, x - y, 'result-set1', 123.456]; |
| | else |
| | return [y, x + y, 'result-set2']; |
+----------+---------------------------------------------------------+
| ?: | Ternary conditional statement, similar to that of the |
| | above denoted if-statement. |
| | eg: |
| | 1. x ? y : z |
| | 2. x + 1 > 2y ? z + 1 : (w / v) |
| | 3. min(x,y) > z ? (x < y + 1) ? x : y : (w * v) |
+----------+---------------------------------------------------------+
| ~ | Evaluate each sub-expression, then return as the result |
| | the value of the last sub-expression. This is sometimes |
| | known as multiple sequence point evaluation. |
| | eg: |
| | ~(i := x + 1, j := y / z, k := sin(w/u)) == (sin(w/u))) |
| | ~{i := x + 1; j := y / z; k := sin(w/u)} == (sin(w/u))) |
+----------+---------------------------------------------------------+
| [*] | Evaluate any consequent for which its case statement is |
| | true. The return value will be either zero or the result|
| | of the last consequent to have been evaluated. |
| | eg: |
| | [*] |
| | { |
| | case (x + 1) > (y - 2) : x := z / 2 + sin(y / pi); |
| | case (x + 2) < abs(y + 3) : w / 4 + min(5y,9); |
| | case (x + 3) == (y * 4) : y := abs(z / 6) + 7y; |
| | } |
+----------+---------------------------------------------------------+
| [] | The vector size operator returns the size of the vector |
| | being actioned. |
| | eg: |
| | 1. v[] |
| | 2. max_size := max(v0[],v1[],v2[],v3[]) |
+----------+---------------------------------------------------------+
Note: In the tables above, the symbols x, y, z, w, u and v where
appropriate may represent any of one the following:
1. Literal numeric/string value
2. A variable
3. A vector element
4. A vector
5. A string
6. An expression comprised of [1], [2] or [3] (eg: 2 + x / vec[3])
[09 - Fundamental Types]
ExprTk supports three fundamental types which can be used freely in
expressions. The types are as follows:
(1) Scalar
(2) Vector
(3) String
(1) Scalar Type
The scalar type is a singular numeric value. The underlying type is
that used to specialize the ExprTk components (float, double, long
double, MPFR et al).
(2) Vector Type
The vector type is a fixed size sequence of scalar values. A vector
can be indexed resulting in a scalar value. Operations between a
vector and scalar will result in a vector with a size equal to that of
the original vector, whereas operations between vectors will result in
a vector of size equal to that of the smaller of the two.
(3) String Type
The string type is a variable length sequence of 8-bit chars. Strings
can be assigned and concatenated to one another, they can also be
manipulated via sub-ranges using the range definition syntax. Strings
however can not interact with scalar or vector types.
[10 - COMPONENTS]
There are three primary components, that are specialized upon a given
numeric type, which make up the core of ExprTk. The components are as
follows:
(1) Symbol Table exprtk::symbol_table<NumericType>
(2) Expression exprtk::expression<NumericType>
(3) Parser exprtk::parser<NumericType>
(1) Symbol Table
A structure that is used to store references to variables, constants
and functions that are to be used within expressions. Furthermore in
the context of composited recursive functions the symbol table can
also be thought of as a simple representation of a stack specific for
the expression(s) that reference it. The following is a list of the
types a symbol table can handle:
(a) Numeric variables
(b) Numeric constants
(c) Numeric vector elements
(d) String variables
(e) String constants
(f) Functions
(g) Vararg functions
During the compilation process if an expression is found to require
any of the elements noted above, the expression's associated
symbol_table will be queried for the element and if present a
reference to the element will be embedded within the expression's AST.
This allows for the original element to be modified independently of
the expression instance and to also allow the expression to be
evaluated using the current value of the element.
The example below demonstrates the relationship between variables,
symbol_table and expression. Note the variables are modified as they
normally would in a program, and when the expression is evaluated the
current values assigned to the variables will be used.
typedef exprtk::symbol_table<double> symbol_table_t;
typedef exprtk::expression<double> expression_t;
typedef exprtk::parser<double> parser_t;
symbol_table_t symbol_table;
expression_t expression;
parser_t parser;
double x = 0;
double y = 0;
std::string expression_string = "x * y + 3";
symbol_table.add_variable("x",x);
symbol_table.add_variable("y",y);
expression.register_symbol_table(symbol_table);
parser.compile(expression_string,expression);
x = 1.0;
y = 2.0;
expression.value(); // 1 * 2 + 3
x = 3.7;
expression.value(); // 3.7 * 2 + 3
y = -9.0;
expression.value(); // 3.7 * -9 + 3
// 'x * -9 + 3' for x in range of [0,100) in steps of 0.0001
for (x = 0.0; x < 100.0; x += 0.0001)
{
expression.value(); // x * -9 + 3
}
Note: It is possible to register multiple symbol_tables with a single
expression object. In the event an expression has multiple symbol
tables, and where there exists conflicts between symbols, the
compilation stage will resolve the conflicts based on the order of
registration of the symbol_tables to the expression.
typedef exprtk::symbol_table<double> symbol_table_t;
typedef exprtk::expression<double> expression_t;
typedef exprtk::parser<double> parser_t;
symbol_table_t symbol_table0;
symbol_table_t symbol_table1;
expression_t expression;
parser_t parser;
double x0 = 123.0;
double x1 = 678.0;
std::string expression_string = "x + 1";
symbol_table0.add_variable("x",x0);
symbol_table1.add_variable("x",x1);
expression.register_symbol_table(symbol_table0);
expression.register_symbol_table(symbol_table1);
parser.compile(expression_string,expression);
expression.value(); // 123 + 1
(2) Expression
A structure that holds an abstract syntax tree or AST for a specified
expression and is used to evaluate said expression. Evaluation of the
expression is accomplished by performing a post-order traversal of the
AST. If a compiled Expression uses variables or user defined
functions, it will have an associated Symbol Table, which will contain
references to said variables, functions or strings. An example AST
structure for the denoted expression is as follows:
Expression: z := (x + y^-2.345) * sin(pi / min(w - 7.3,v))
[Root]
|
[Assignment]
________/ \_____
/ \
Variable(z) [Multiplication]
____________/ \___________
/ \
/ [Unary-Func(sin)]
[Addition] |
____/ \____ [Division]
/ \ ___/ \___
Variable(x) [Exponentiation] / \
______/ \______ Constant(pi) [Binary-Func(min)]
/ \ ____/ \____
Variable(y) [Negation] / \
| / Variable(v)
Constant(2.345) /
/
[Subtraction]
____/ \____
/ \
Variable(w) Constant(7.3)
The above denoted AST will be evaluated in the following order:
(01) Load Variable (z) (10) Load Constant (7.3)
(02) Load Variable (x) (11) Subtraction (09 & 10)
(03) Load Variable (y) (12) Load Variable (v)
(04) Load Constant (2.345) (13) Min (11 & 12)
(05) Negation (04) (14) Division (08 & 13)
(06) Exponentiation (03 & 05) (15) Sin (14)
(07) Addition (02 & 06) (16) Multiplication (07 & 15)
(08) Load Constant (pi) (17) Assignment (01 & 16)
(09) Load Variable (w)
(3) Parser
A structure which takes as input a string representation of an
expression and attempts to compile said input with the result being an
instance of Expression. If an error is encountered during the
compilation process, the parser will stop compiling and return an
error status code, with a more detailed description of the error(s)
and its location within the input provided by the 'get_error'
interface.
[11 - COMPILATION OPTIONS]
The exprtk::parser when being instantiated takes as input a set of
options to be used during the compilation process of expressions.
An example instantiation of exprtk::parser where only the joiner,
commutative and strength reduction options are enabled is as follows:
typedef exprtk::parser<NumericType>::settings_t settings_t;
std::size_t compile_options = settings_t::e_joiner +
settings_t::e_commutative_check +
settings_t::e_strength_reduction;
parser_t parser(compile_options);
Currently seven types of compile time options are supported, and
enabled by default. The options and their explanations are as follows:
(1) Replacer
(2) Joiner
(3) Numeric Check
(4) Bracket Check
(5) Sequence Check
(6) Commutative Check
(7) Strength Reduction Check
(1) Replacer (e_replacer)
Enable replacement of specific tokens with other tokens. For example
the token "true" of type symbol will be replaced with the numeric
token of value one.
(a) (x < y) == true ---> (x < y) == 1
(b) false == (x > y) ---> 0 == (x > y)
(2) Joiner (e_joiner)
Enable joining of multi-character operators that may have been
incorrectly disjoint in the string representation of the specified
expression. For example the consecutive tokens of ">" "=" will become
">=" representing the "greater than or equal to" operator. If not
properly resolved the original form will cause a compilation error.
The following is a listing of the scenarios that the joiner can
handle:
(a) '>' '=' ---> '>=' (gte)
(b) '<' '=' ---> '<=' (lte)
(c) '=' '=' ---> '==' (equal)
(d) '!' '=' ---> '!=' (not-equal)
(e) '<' '>' ---> '<>' (not-equal)
(f) ':' '=' ---> ':=' (assignment)
(g) '+' '=' ---> '+=' (addition assignment)
(h) '-' '=' ---> '-=' (subtraction assignment)
(i) '*' '=' ---> '*=' (multiplication assignment)
(j) '/' '=' ---> '/=' (division assignment)
(k) '%' '=' ---> '%=' (modulo assignment)
(l) '+' '-' ---> '-' (subtraction)
(m) '-' '+' ---> '-' (subtraction)
(n) '-' '-' ---> '+' (addition)
(o) '<=' '>' ---> '<=>' (swap)
An example of the transformation that takes place is as follows:
(a) (x > = y) and (z ! = w) ---> (x >= y) and (z != w)
(3) Numeric Check (e_numeric_check)
Enable validation of tokens representing numeric types so as to catch
any errors prior to the costly process of the main compilation step
commencing.
(4) Bracket Check (e_bracket_check)
Enable the check for validating the ordering of brackets in the
specified expression.
(5) Sequence Check (e_sequence_check)
Enable the check for validating that sequences of either pairs or
triplets of tokens make sense. For example the following sequence of
tokens when encountered will raise an error:
(a) (x + * 3) ---> sequence error
(6) Commutative Check (e_commutative_check)
Enable the check that will transform sequences of pairs of tokens that
imply a multiplication operation. The following are some examples of
such transformations:
(a) 2x ---> 2 * x
(b) 25x^3 ---> 25 * x^3
(c) 3(x + 1) ---> 3 * (x + 1)
(d) (x + 1)4 ---> (x + 1) * 4
(e) 5foo(x,y) ---> 5 * foo(x,y)
(f) foo(x,y)6 + 1 ---> foo(x,y) * 6 + 1
(g) (4((2x)3)) ---> 4 * ((2 * x) * 3)
(h) w(x) + (y)z ---> w * x + y * z
(7) Strength Reduction Check (e_strength_reduction)
Enable the use of strength reduction optimisations during the
compilation process. In ExprTk strength reduction optimisations
predominantly involve transforming sub-expressions into other forms
that are algebraically equivalent yet less costly to compute. The
following are examples of the various transformations that can occur:
(a) (x / y) / z ---> x / (y * z)
(b) (x / y) / (z / w) ---> (x * w) / (y * z)
(c) (2 * x) - (2 * y) ---> 2 * (x - y)
(d) (2 / x) / (3 / y) ---> (2 / 3) / (x * y)
(e) (2 * x) * (3 * y) ---> (2 * 3) * (x * y)
Note:
When using strength reduction in conjunction with expressions whose
inputs or sub-expressions may result in values nearing either of the
bounds of the underlying numeric type (eg: double), there may be the
possibility of a decrease in the precision of results.
In the following example the given expression which represents an
attempt at computing the average between x and y will be transformed
as follows:
(0.5 * x) + (y * 0.5) ---> 0.5 * (x + y)
There may be situations where the above transformation will cause
numerical overflows and that the original form of the expression is
desired over the strength reduced form. In these situations it is best
to turn off strength reduction optimisations or to use a type with a
larger numerical bound.
[12 - SPECIAL FUNCTIONS]
The purpose of special functions in ExprTk is to provide compiler
generated equivalents of common mathematical expressions which can be
invoked by using the 'special function' syntax (eg: $f12(x,y,z) or
$f82(x,y,z,w)).
Special functions dramatically decrease the total evaluation time of
expressions which would otherwise have been written using the common
form by reducing the total number of nodes in the evaluation tree of
an expression and by also leveraging the compiler's ability to
correctly optimize such expressions for a given architecture.
3-Parameter 4-Parameter
+-------------+-------------+ +--------------+------------------+
| Prototype | Operation | | Prototype | Operation |
+-------------+-------------+ +--------------+------------------+
$f00(x,y,z) | (x + y) / z $f48(x,y,z,w) | x + ((y + z) / w)
$f01(x,y,z) | (x + y) * z $f49(x,y,z,w) | x + ((y + z) * w)
$f02(x,y,z) | (x + y) - z $f50(x,y,z,w) | x + ((y - z) / w)
$f03(x,y,z) | (x + y) + z $f51(x,y,z,w) | x + ((y - z) * w)
$f04(x,y,z) | (x - y) + z $f52(x,y,z,w) | x + ((y * z) / w)
$f05(x,y,z) | (x - y) / z $f53(x,y,z,w) | x + ((y * z) * w)
$f06(x,y,z) | (x - y) * z $f54(x,y,z,w) | x + ((y / z) + w)
$f07(x,y,z) | (x * y) + z $f55(x,y,z,w) | x + ((y / z) / w)
$f08(x,y,z) | (x * y) - z $f56(x,y,z,w) | x + ((y / z) * w)
$f09(x,y,z) | (x * y) / z $f57(x,y,z,w) | x - ((y + z) / w)
$f10(x,y,z) | (x * y) * z $f58(x,y,z,w) | x - ((y + z) * w)
$f11(x,y,z) | (x / y) + z $f59(x,y,z,w) | x - ((y - z) / w)
$f12(x,y,z) | (x / y) - z $f60(x,y,z,w) | x - ((y - z) * w)
$f13(x,y,z) | (x / y) / z $f61(x,y,z,w) | x - ((y * z) / w)
$f14(x,y,z) | (x / y) * z $f62(x,y,z,w) | x - ((y * z) * w)
$f15(x,y,z) | x / (y + z) $f63(x,y,z,w) | x - ((y / z) / w)
$f16(x,y,z) | x / (y - z) $f64(x,y,z,w) | x - ((y / z) * w)
$f17(x,y,z) | x / (y * z) $f65(x,y,z,w) | ((x + y) * z) - w
$f18(x,y,z) | x / (y / z) $f66(x,y,z,w) | ((x - y) * z) - w
$f19(x,y,z) | x * (y + z) $f67(x,y,z,w) | ((x * y) * z) - w
$f20(x,y,z) | x * (y - z) $f68(x,y,z,w) | ((x / y) * z) - w
$f21(x,y,z) | x * (y * z) $f69(x,y,z,w) | ((x + y) / z) - w
$f22(x,y,z) | x * (y / z) $f70(x,y,z,w) | ((x - y) / z) - w
$f23(x,y,z) | x - (y + z) $f71(x,y,z,w) | ((x * y) / z) - w
$f24(x,y,z) | x - (y - z) $f72(x,y,z,w) | ((x / y) / z) - w
$f25(x,y,z) | x - (y / z) $f73(x,y,z,w) | (x * y) + (z * w)
$f26(x,y,z) | x - (y * z) $f74(x,y,z,w) | (x * y) - (z * w)
$f27(x,y,z) | x + (y * z) $f75(x,y,z,w) | (x * y) + (z / w)
$f28(x,y,z) | x + (y / z) $f76(x,y,z,w) | (x * y) - (z / w)
$f29(x,y,z) | x + (y + z) $f77(x,y,z,w) | (x / y) + (z / w)
$f30(x,y,z) | x + (y - z) $f78(x,y,z,w) | (x / y) - (z / w)
$f31(x,y,z) | x * y^2 + z $f79(x,y,z,w) | (x / y) - (z * w)
$f32(x,y,z) | x * y^3 + z $f80(x,y,z,w) | x / (y + (z * w))
$f33(x,y,z) | x * y^4 + z $f81(x,y,z,w) | x / (y - (z * w))
$f34(x,y,z) | x * y^5 + z $f82(x,y,z,w) | x * (y + (z * w))
$f35(x,y,z) | x * y^6 + z $f83(x,y,z,w) | x * (y - (z * w))
$f36(x,y,z) | x * y^7 + z $f84(x,y,z,w) | x*y^2 + z*w^2
$f37(x,y,z) | x * y^8 + z $f85(x,y,z,w) | x*y^3 + z*w^3
$f38(x,y,z) | x * y^9 + z $f86(x,y,z,w) | x*y^4 + z*w^4
$f39(x,y,z) | x * log(y)+z $f87(x,y,z,w) | x*y^5 + z*w^5
$f40(x,y,z) | x * log(y)-z $f88(x,y,z,w) | x*y^6 + z*w^6
$f41(x,y,z) | x * log10(y)+z $f89(x,y,z,w) | x*y^7 + z*w^7
$f42(x,y,z) | x * log10(y)-z $f90(x,y,z,w) | x*y^8 + z*w^8
$f43(x,y,z) | x * sin(y)+z $f91(x,y,z,w) | x*y^9 + z*w^9
$f44(x,y,z) | x * sin(y)-z $f92(x,y,z,w) | (x and y) ? z : w
$f45(x,y,z) | x * cos(y)+z $f93(x,y,z,w) | (x or y) ? z : w
$f46(x,y,z) | x * cos(y)-z $f94(x,y,z,w) | (x < y) ? z : w
$f47(x,y,z) | x ? y : z $f95(x,y,z,w) | (x <= y) ? z : w
$f96(x,y,z,w) | (x > y) ? z : w
$f97(x,y,z,w) | (x >= y) ? z : w
$f98(x,y,z,w) | (x == y) ? z : w
$f99(x,y,z,w) | x*sin(y)+z*cos(w)
[13 - VARIABLE , VECTOR & STRING DEFINITION]
ExprTk supports the definition of expression local variables, vectors
and strings. The definitions must be unique as shadowing is not
allowed and object life-times are based on scope. Definitions use the
following general form:
var <name> := <initialiser>;
(1) Variable Definition
Variables are of numeric type denoting a single value. They can be
explicitly initialised to a value, otherwise they will be defaulted to
zero. The following are examples of variable definitions:
(a) Initialise x to zero
var x;
(b) Initialise y to three
var y := 3;
(c) Initialise z to the expression
var z := if(max(1,x + y) > 2,w,v);
(2) Vector Definition
Vectors are arrays of a common numeric type. The elements in a vector
can be explicitly initialised, otherwise they will all be defaulted to
zero. The following are examples of vector definitions:
(a) Initialise all values to zero
var x[3];
(b) Initialise all values to zero
var x[3] := {};
(c) Initialise all values to given expression
var x[3] := [123 + 3y + sin(w/z)];
(d) Initialise the first two values, all other elements to zero
var x[3] := { 1 + x[2], sin(y[0] / x[]) + 3 };
(e) Initialise the first three (all) values
var x[3] := { 1, 2, 3 };
(f) Error as there are too many initialisers
var x[3] := { 1, 2, 3, 4 };
(g) Error as a vector of size zero is not allowed.
var x[0];
(3) String Definition
Strings are a sequence of 8-bit characters. They can only be defined
with an explicit initialisation value. The following are examples of
string variable definitions:
(a) Initialise to a string
var x := 'abc';
(b) Initialise to a string expression
var x := 'abc' + '123';
(c) Initialise to a string range
var x := 'abc123'[2:4];
(d) Initialise to another string variable
var x := 'abc';
var y := x;
(e) Initialise to another string variable range
var x := 'abc123';
var y := x[2:4];
(f) Initialise to a string expression
var x := 'abc';
var y := x + '123';
(g) Initialise to a string expression range
var x := 'abc';
var y := (x + '123')[1:3];
(4) Return Value
Variable and vector definitions have a return value. In the case of
variable definitions, the value to which the variable is initialised
will be returned. Where as for vectors, the value of the first element
(eg: v[0]) will be returned.
(5) Variable/Vector Assignment
The value of a variable can be assigned to a vector and a vector or a
vector expression can be assigned to a variable.
(a) Variable To Vector:
Every element of the vector is assigned the value of the variable
or expression.
var x := 3;
var y[3] := { 1, 2, 3 };
y := x + 1;
(b) Vector To Variable:
The variable is assigned the value of the first element of the
vector (aka vec[0])
var x := 3;
var y[3] := { 1, 2, 3 };
x := y + 1;
Note: During the expression compilation phase, tokens are classified
based on the following priorities:
(a) Reserved keywords or operators (+, -, and, or, etc)
(b) Base functions (abs, sin, cos, min, max etc)
(c) Symbol table variables
(d) Expression local defined variables
(e) Symbol table functions
(f) Unknown symbol resolver based variables
[14 - VECTOR PROCESSING]
ExprTk provides support for various forms of vector oriented
arithmetic, inequalities and processing. The various supported pairs
are as follows:
(a) vector and vector (eg: v0 + v1)
(b) vector and scalar (eg: v + 33)
(c) scalar and vector (eg: 22 * v)
The following is a list of operations that can be used in conjunction
with vectors:
(a) Arithmetic: +, -, *, /, %
(b) Exponentiation: vector ^ scalar
(c) Assignment: :=, +=, -=, *=, /=, %=, <=>
(d) Inequalities: <, <=, >, >=, ==, =
(e) Unary operations:
abs, acos, acosh, asin, asinh, atan, atanh, ceil, cos, cosh,
cot, csc, deg2grad, deg2rad, erf, erfc, exp, expm1, floor,
frac, grad2deg, log, log10, log1p, log2, rad2deg, round, sec,
sgn, sin, sinc, sinh, sqrt, swap, tan, tanh, trunc
(f) Aggregate and Reduce operations:
avg, max, min, mul, sum
Note: When one of the above described operations is being performed
between two vectors, the operation will only span the size of the
smallest vector. The elements of the larger vector outside of the
range will not be included.
The following simple example demonstrates the vector processing
capabilities by computing the dot-product of the vectors v0 and v1 and
then assigning it to the variable v0dotv1:
var v0[3] := { 1, 2, 3 };
var v1[3] := { 4, 5, 6 };
var v0dotv1 := sum(v0 * v1);
The following is a for-loop based implementation that is equivalent to
the previously mentioned dot-product computation expression:
var v0[3] := { 1, 2, 3 };
var v1[3] := { 4, 5, 6 };
var v0dotv1;
for (var i := 0; i < min(v0[],v1[]); i += 1)
{
v0dotv1 += (v0[i] * v1[i]);
}
Note: In the scenario of inequalities between two vectors, the result
is not a vector but rather a singular variable denoting a boolean
state of either 'true' or 'false' depending on the nature of the
inequality.
var x[3] := { 1, 1, 1 };
var y[3] := { 3, 2, 1 };
y > x == false
Note: When the aggregate operations denoted above are used in
conjunction with a vector or vector expression, the return value is
not a vector but rather a single value.
var x[3] := { 1, 2, 3 };
sum(x) == 6
sum(1 + 2x) == 15
avg(3x + 1) == 7
min(1 / x) == (1 / 3)
max(x / 2) == (3 / 2)
[15 - USER DEFINED FUNCTIONS]
ExprTk provides a means whereby custom functions can be defined and
utilized within expressions. The concept requires the user to
provide a reference to the function coupled with an associated name
that will be invoked within expressions. Functions may take numerous
inputs but will always return a single value of the underlying numeric
type.
During expression compilation when required the reference to the
function will be obtained from the associated symbol_table and be
embedded into the expression.
There are five types of function interface:
+---+----------------------+-------------+
| # | Name | Return Type |
+---+----------------------+-------------+
| 1 | ifunction | Scalar |
| 2 | ivararg_function | Scalar |
| 3 | igeneric_function | Scalar |
| 4 | igeneric_function II | String |
| 5 | function_compositor | Scalar |
+---+----------------------+-------------+
(1) ifunction
This interface supports zero to 20 input parameters. The usage
requires a custom function be derived from ifunction and to override
one of the 21 function operators. As part of the constructor the
custom function will define how many parameters it expects to handle.
The following example defines a 3 parameter function called 'foo':
template <typename T>
struct foo : public exprtk::ifunction<T>
{
foo() : exprtk::ifunction<T>(3)
{}
T operator()(const T& v1, const T& v2, const T& v3)
{
return T(1) + (v1 * v2) / T(v3);
}
};
(2) ivararg_function
This interface supports a variable number of arguments as input into
the function. The function operator interface uses a std::vector
specialized upon type T to facilitate parameter passing. The following
example defines a vararg function called 'boo':
template <typename T>
struct boo : public exprtk::ivararg_function<T>
{
inline T operator()(const std::vector<T>& arglist)
{
T result = T(0);
for (std::size_t i = 0; i < arglist.size(); ++i)
{
result += arglist[i] / arglist[i > 0 ? (i - 1) : 0];
}
return result;
}
};
(3) igeneric_function
This interface supports a variable number of arguments and types as
input into the function. The function operator interface uses a
std::vector specialized upon the type_store type to facilitate
parameter passing.
Scalar <-- function(i_0, i_1, i_2....., i_N)
The fundamental types that can be passed into the function as
parameters and their views are as follows:
(1) Scalar - scalar_view
(2) Vector - vector_view
(3) String - string_view
The above denoted type views provide non-const reference-like access
to each parameter, as such modifications made to the input parameters
will persist after the function call has completed. The following
example defines a generic function called 'too':
template <typename T>
struct too : public exprtk::igeneric_function<T>
{
typedef typename exprtk::igeneric_function<T>::parameter_list_t
parameter_list_t;
too()
{}
inline T operator()(parameter_list_t parameters)
{
for (std::size_t i = 0; i < parameters.size(); ++i)
{
...
}
return T(0);
}
};
In the example above, the input 'parameters' to the function operator,
parameter_list_t, is a type of std::vector of type_store. Each
type_store instance has a member called 'type' which holds the
enumeration pertaining to the underlying type of the type_store. There
are three type enumerations:
(1) e_scalar - literals, variables, vector elements, expressions
eg: 123.456, x, vec[3x + 1], 2x + 3
(2) e_vector - vectors, vector expressions
eg: vec1, 2 * vec1 + vec2 / 3
(3) e_string - strings, string literals and range variants of both
eg: 'AString', s0, 'AString'[x:y], s1[1 + x:] + 'AString'
Each of the parameters can be accessed using its designated view. A
typical loop for processing the parameters is as follows:
inline T operator()(parameter_list_t parameters)
{
typedef typename exprtk::igeneric_function<T>::generic_type
generic_type;
typedef typename generic_type::scalar_view scalar_t;
typedef typename generic_type::vector_view vector_t;
typedef typename generic_type::string_view string_t;
for (std::size_t i = 0; i < parameters.size(); ++i)
{
generic_type& gt = parameters[i];
if (generic_type::e_scalar == gt.type)
{
scalar_t x(gt);
...
}
else if (generic_type::e_vector == gt.type)
{
vector_t vector(gt);
...
}
else if (generic_type::e_string == gt.type)
{
string_t string(gt);
...
}
}
return T(0);
}
Most often than not a custom generic function will require a specific
sequence of parameters, rather than some arbitrary sequence of types.
In those situations, ExprTk can perform compile-time type checking to
validate that function invocations are carried out using the correct
sequence of parameters. Furthermore performing the checks at compile
-time rather than at run-time (aka every time the function is invoked)
will result in expression evaluation performance gains.
Compile-time type checking of input parameters can be requested by
passing a string to the constructor of the igeneric_function that
represents the required sequence of parameter types. When no parameter
sequence is provided, it is implied the function can accept a variable
number of parameters comprised of any of the fundamental types.
Each fundamental type has an associated character. The following is a
listing of said characters and their meanings:
(1) T - Scalar
(2) V - Vector
(3) S - String
(4) ? - Any type (Scalar, Vector or String)
(5) * - Wildcard operator
(6) | - Parameter sequence delimiter
No other characters other than the six denoted above may be included
in the parameter sequence definition. If any such invalid characters
do exist, registration of the associated generic function to a symbol
table ('add_function' method) will fail. If the parameter sequence is
modified resulting in it becoming invalid after having been added to
the symbol table but before the compilation step, a compilation error
will be incurred.
The following example demonstrates a simple generic function
implementation with a user specified parameter sequence:
template <typename T>
struct moo : public exprtk::igeneric_function<T>
{
typedef typename exprtk::igeneric_function<T>::parameter_list_t
parameter_list_t;
moo()
: exprtk::igeneric_function<T>("SVTT")
{}
inline T operator()(parameter_list_t parameters)
{
...
}
};
In the example above the generic function 'moo' expects exactly four
parameters in the following sequence:
(1) String
(2) Vector
(3) Scalar
(4) Scalar
(4) igeneric_function II
This interface is identical to the igeneric_function, in that in can
consume an arbitrary number of parameters of varying type, but the
difference being that the function returns a string and as such is
treated as a string when invoked within expressions. As a result the
function call can alias a string and interact with other strings in
situations such as concatenation and equality operations.
String <-- function(i_0, i_1, i_2....., i_N)
The following example defines a generic function named 'toupper' with
the string return type function operator being explicitly overridden:
template <typename T>
struct toupper : public exprtk::igeneric_function<T>
{
typedef exprtk::igeneric_function<T> igenfunct_t
typedef typename igenfunct_t::generic_type generic_t;
typedef typename igenfunct_t::parameter_list_t parameter_list_t;
typedef typename generic_t::string_view string_t;
toupper()
: exprtk::igeneric_function<T>("S",igenfunct_t::e_rtrn_string)
{}
inline T operator()(std::string& result,
parameter_list_t parameters)
{
result.clear();
string_t string(params[0]);
for (std::size_t i = 0; i < string.size(); ++i)
{
result += std::toupper(string[i]);
}
return T(0);
}
};
In the example above the generic function 'toupper' expects only one
input parameter of type string, as noted by the parameter sequence
string passed during the constructor. Furthermore a second parameter
is passed to the constructor indicating that it should be treated as a
string returning function - by default it is assumed to be a scalar
returning function.
When executed, the function will return as a result a copy of the
input string converted to uppercase form. An example expression using
the toupper function registered as the symbol 'toupper' is as follows:
"'ABCDEF' == toupper('aBc') + toupper('DeF')"
Note: When adding a string type returning generic function to a symbol
table the 'add_function' is invoked. The example below demonstrates
how this can be done:
toupper<T> tu;
exprtk::symbol_table<T> symbol_table;
symbol_table.add_function("toupper",tu);
Note: Two further refinements to the type checking facility are the
possibilities of a variable number of common types which can be
accomplished by using a wildcard '*' and a special 'any type' which is
done using the '?' character. It should be noted that the wildcard
operator is associated with the previous type in the sequence and
implies one or more of that type.
template <typename T>
struct zoo : public exprtk::igeneric_function<T>
{
typedef typename exprtk::igeneric_function<T>::parameter_list_t
parameter_list_t;
zoo()
: exprtk::igeneric_function<T>("SVT*V?")
{}
inline T operator()(parameter_list_t parameters)
{
...
}
};
In the example above the generic function 'zoo' expects at least five
parameters in the following sequence:
(1) String
(2) Vector
(3) One or more Scalars
(4) Vector
(5) Any type (one type of either a scalar, vector or string)
A final piece of type checking functionality is available for the
scenarios where a single function name is intended to be used for
multiple distinct parameter sequences, another name for this feature
is function overloading. The parameter sequences are passed to the
constructor as a single string delimited by the pipe '|' character.
Two specific overrides of the function operator are provided one for
standard generic functions and one for string returning functions. The
overrides are as follows:
// Scalar <-- function(psi,i_0,i_1,....,i_N)
inline T operator()(const std::size_t& ps_index,
parameter_list_t parameters)
{
...
}
// String <-- function(psi,i_0,i_1,....,i_N)
inline T operator()(const std::size_t& ps_index,
std::string& result,
parameter_list_t parameters)
{
...
}
When the function operator is invoked the 'ps_index' parameter will
have as its value the index of the parameter sequence that matches the
specific invocation. This way complex and time consuming type checking
conditions need not be executed in the function itself but rather a
simple and efficient dispatch to a specific implementation for that
particular parameter sequence can be performed.
template <typename T>
struct roo : public exprtk::igeneric_function<T>
{
typedef typename exprtk::igeneric_function<T>::parameter_list_t
parameter_list_t;
moo()
: exprtk::igeneric_function<T>("SVTT|SS|TTV|S?V*S")
{}
inline T operator()(const std::size_t& ps_index,
parameter_list_t parameters)
{
...
}
};
In the example above there are four distinct parameter sequences that
can be processed by the generic function 'roo'. Any other parameter
sequences will cause a compilation error. The four valid sequences are
as follows:
Sequence-0 Sequence-1 Sequence-2 Sequence-3
'SVTT' 'SS' 'TTV' 'S?V*S'
(1) String (1) String (1) Scalar (1) String
(2) Vector (2) String (2) Scalar (2) Any Type
(3) Scalar (3) Vector (3) One or more Vectors
(4) Scalar (4) String
(5) function_compositor
The function compositor is a factory that allows one to define and
construct a function using ExprTk syntax. The functions are limited to
returning a single scalar value and consuming up to six parameters as
input.
All composited functions are registered with a symbol table, allowing
them to call other functions that have been registered with the symbol
table instance. Furthermore the functions can be recursive in nature
due to the inherent function prototype forwarding that occurs during
construction. The following example defines, by using two different
methods, composited functions and implicitly registering the functions
with the denoted symbol table.
typedef exprtk::symbol_table<T> symbol_table_t;
typedef exprtk::function_compositor<T> compositor_t;
typedef typename compositor_t::function function_t;
symbol_table_t symbol_table;
compositor_t compositor(symbol_table);
// define function koo0(v1,v2) { ... }
compositor
.add(
function_t(
"koo0",
" 1 + cos(v1 * v2) / 3;",
"v1","v2"));
// define function koo1(x,y,z) { ... }
compositor
.add(function_t()
.name("koo1")
.var("x").var("y").var("z")
.expression("1 + cos(x * y) / z;"));
(6) Using Functions In Expressions
For the above denoted custom and composited functions to be used in an
expression, an instance of each function needs to be registered with a
symbol_table that has been associated with the expression instance.
The following demonstrates how all the pieces are put together:
typedef exprtk::symbol_table<double> symbol_table_t;
typedef exprtk::expression<double> expression_t;
typedef exprtk::parser<double> parser_t;
typedef exprtk::function_compositor<T> compositor_t;
typedef typename compositor_t::function function_t;
foo<double> f;
boo<double> b;
too<double> t;
toupper<double> tu;
symbol_table_t symbol_table;
compositor_t compositor(symbol_table);
symbol_table.add_function("foo",f);
symbol_table.add_function("boo",b);
symbol_table.add_function("too",t);
symbol_table.add_function("toupper",
tu,
symbol_table_t::e_ft_strfunc);
compositor
.add(function_t()
.name("koo")
.var("v1")
.var("v2")
.expression("1 + cos(v1 * v2) / 3;"));
expression_t expression;
expression.register_symbol_table(symbol_table);
std::string expression_str =
" if (foo(1,2,3) + boo(1) > boo(1/2,2/3,3/4,4/5)) "
" koo(3,4); "
" else "
" too(2 * v1 + v2 / 3, 'abcdef'[2:4], 3.3); "
" ";
parser_t parser;
parser.compile(expression_str,expression);
expression.value();
(7) Function Side-Effects
All function calls are assumed to have side-effects by default. This
assumption implicitly disables constant folding optimisations when all
parameters being passed to the function are deduced as being constants
at compile time.
If it is certain that the function being registered does not have any
side effects and can be correctly constant folded where appropriate,
then during the construction of the function the side-effect trait of
the function can be disabled.
template <typename T>
struct foo : public exprtk::ifunction<T>
{
foo() : exprtk::ifunction<T>(3)
{
exprtk::disable_has_side_effects(*this);
}
T operator()(const T& v1, const T& v2, const T& v3)
{ ... }
};
(8) Zero Parameter Functions
When either an ifunction, ivararg_function or igeneric_function
derived type is defined with zero number of parameters, there are two
calling conventions within expressions that are allowed. For a
function named 'foo' with zero input parameters the calling styles are
as follows:
(1) x + sin(foo()- 2) / y
(2) x + sin(foo - 2) / y
By default the zero parameter trait is disabled. In order to enable
it, a process similar to that of enabling of the side effect trait is
carried out:
template <typename T>
struct foo : public exprtk::ivararg_function<T>
{
foo()
{
exprtk::enable_zero_parameters(*this);
}
inline T operator()(const std::vector<T>& arglist)
{ ... }
};
[16 - EXPRESSION DEPENDENTS]
Any expression that is not a literal (aka constant) will have
dependencies. The types of 'dependencies' an expression can have are
as follows:
(a) Variables
(b) Vectors
(c) Strings
(d) Functions
(e) Assignments
In the following example the denoted expression has its various
dependencies listed:
z := abs(x + sin(2 * pi / y))
(a) Variables: x, y, z and pi
(b) Functions: abs, sin
(c) Assignments: z
ExprTk allows for the derivation of expression dependencies via the
'dependent_entity_collector' (DEC). When activated either through
'compile_options' at the construction of the parser or through calls
to enabler methods just prior to compilation, the DEC will proceed to
collect any of the relevant types that are encountered during the
parsing phase. Once the compilation process has successfully
completed, the caller can then obtain a list of symbols and their
associated types from the DEC.
The kinds of questions one can ask regarding the dependent entities
within an expression are as follows:
* What user defined or local variables, vectors or strings are used?
* What functions or custom user functions are used?
* Which variables, vectors or strings have values assigned to them?
The following example demonstrates usage of the DEC in determining the
dependents of the given expression:
typedef typename parser_t::
dependent_entity_collector::symbol_t symbol_t;
std::string expression_string =
"z := abs(x + sin(2 * pi / y))";
T x,y,z;
parser_t parser;
symbol_table_t symbol_table;
symbol_table.add_variable("x",x);
symbol_table.add_variable("y",y);
symbol_table.add_variable("z",z);
expression_t expression;
expression.register_symbol_table(symbol_table);
//Collect only variable and function symbols
parser.dec().collect_variables() = true;
parser.dec().collect_functions() = true;
if (!parser.compile(expression_string,expression))
{
// error....
}
std::deque<symbol_t> symbol_list;
parser.dec().symbols(symbol_list);
for (std::size_t i = 0; i < symbol_list.size(); ++i)
{
symbol_t& symbol = symbol_list[i];
switch (symbol.second)
{
case parser_t::e_st_variable : ... break;
case parser_t::e_st_vector : ... break;
case parser_t::e_st_string : ... break;
case parser_t::e_st_function : ... break;
}
}
Note: The 'symbol_t' type is a std::pair comprising of the symbol name
(std::string) and the associated type of the symbol as denoted by the
cases in the switch statement.
Having particular symbols (variable or function) present in an
expression is one form of dependency. Another and just as interesting
and important type of dependency is that of assignments. Assignments
are the set of dependent symbols that 'may' have their values modified
within an expression. The following are example expressions and their
associated assignments:
Assignments Expression
(1) x x := y + z
(2) x, y x += y += z
(3) x, y, z x := y += sin(z := w + 2)
(4) z, w if (x > y, z := x + 2, w := 'A String')
(5) None x + y + z
Note: In expression 4, both variables 'z' and 'w' are denoted as being
assignments even though only one of them can be modified at the time
of evaluation. Furthermore the determination of which of the two
variables the modification will occur upon can only be known with
certainty at evaluation time and not beforehand, hence both are listed
as being candidates for assignment.
The following builds upon the previous example demonstrating the usage
of the DEC in determining the 'assignments' of the given expression:
//Collect assignments
parser.dec().collect_assignments() = true;
if (!parser.compile(expression_string,expression))
{
// error....
}
std::deque<symbol_t> symbol_list;
parser.dec().assignment_symbols(symbol_list);
for (std::size_t i = 0; i < symbol_list.size(); ++i)
{
symbol_t& symbol = symbol_list[i];
switch (symbol.second)
{
case parser_t::e_st_variable : ... break;
case parser_t::e_st_vector : ... break;
case parser_t::e_st_string : ... break;
}
}
Note: The assignments will only consist of variable types and as such
will not contain symbols denoting functions.
[17 - ENABLING AND DISABLING FEATURES]
The parser can be configured via its settings instance to either allow
or disallow certain features that are available within the ExprTk
grammar. The features fall into one of the following three categories:
(1) Base Functions
(2) Control Flow Structures
(3) Logical Operators
(4) Arithmetic Operators
(5) Inequality Operators
(6) Assignment Operators
(1) Base Functions
The list of available base functions is as follows:
abs, acos, acosh, asin, asinh, atan, atanh, atan2, avg, ceil,
clamp, cos, cosh, cot, csc, equal, erf, erfc, exp, expm1,
floor, frac, hypot, iclamp, like, log, log10, log2, logn,
log1p, mand, max, min, mod, mor, mul, ncdf, pow, root, round,
roundn, sec, sgn, sin, sinc, sinh, sqrt, sum, swap, tan, tanh,
trunc, not_equal, inrange, deg2grad, deg2rad, rad2deg, grad2deg
The above mentioned base functions can be either enabled or disabled
'all' at once, as is demonstrated below:
parser_t parser;
expression_t expression;
parser.settings().disable_all_base_functions();
parser
.compile("2 * abs(2 - 3)",expression); // compilation failure
parser.settings().enable_all_base_functions();
parser
.compile("2 * abs(2 - 3)",expression); // compilation success
One can also enable or disable specific base functions. The following
example demonstrates the disabling of the trigonometric functions
'sin' and 'cos':
parser_t parser;
expression_t expression;
parser.settings()
.disable_base_function(settings_t::e_bf_sin)
.disable_base_function(settings_t::e_bf_cos);
parser
.compile("(sin(x) / cos(x)) == tan(x)",expression); // failure
parser.settings()
.enable_base_function(settings_t::e_bf_sin)
.enable_base_function(settings_t::e_bf_cos);
parser
.compile("(sin(x) / cos(x)) == tan(x)",expression); // success
(2) Control Flow Structures
The list of available control flow structures is as follows:
(a) If or If-Else
(b) Switch statement
(c) For Loop
(d) While Loop
(e) Repeat Loop
The above mentioned control flow structures can be either enabled
or disabled 'all' at once, as is demonstrated below:
parser_t parser;
expression_t expression;
std::string program =
" var x := 0; "
" for (var i := 0; i < 10; i += 1) "
" { "
" x += i; "
" } ";
parser.settings().disable_all_control_structures();
parser
.compile(program,expression); // compilation failure
parser.settings().enable_all_control_structures();
parser
.compile(program,expression); // compilation success
One can also enable or disable specific control flow structures. The
following example demonstrates the disabling of the for-loop control
flow structure:
parser_t parser;
expression_t expression;
std::string program =
" var x := 0; "
" for (var i := 0; i < 10; i += 1) "
" { "
" x += i; "
" } ";
parser.settings()
.disable_control_structure(settings_t::e_ctrl_for_loop);
parser
.compile(program,expression); // failure
parser.settings()
.enable_control_structure(settings_t::e_ctrl_for_loop);
parser
.compile(program,expression); // success
(3) Logical Operators
The list of available logical operators is as follows:
and, nand, nor, not, or, xnor, xor, &, |
The above mentioned logical operators can be either enabled or
disabled 'all' at once, as is demonstrated below:
parser_t parser;
expression_t expression;
parser.settings().disable_all_logic_ops();
parser
.compile("1 or not(0 and 1)",expression); // compilation failure
parser.settings().enable_all_logic_ops();
parser
.compile("1 or not(0 and 1)",expression); // compilation success
One can also enable or disable specific logical operators. The following
example demonstrates the disabling of the 'and' logical operator:
parser_t parser;
expression_t expression;
parser.settings()
.disable_logic_operation(settings_t::e_logic_and);
parser
.compile("1 or not(0 and 1)",expression); // failure
parser.settings()
.enable_logic_operation(settings_t::e_logic_and);
parser
.compile("1 or not(0 and 1)",expression); // success
(4) Arithmetic Operators
The list of available arithmetic operators is as follows:
+, -, *, /, %, ^
The above mentioned arithmetic operators can be either enabled or
disabled 'all' at once, as is demonstrated below:
parser_t parser;
expression_t expression;
parser.settings().disable_all_arithmetic_ops();
parser
.compile("1 + 2 / 3",expression); // compilation failure
parser.settings().enable_all_arithmetic_ops();
parser
.compile("1 + 2 / 3",expression); // compilation success
One can also enable or disable specific arithmetic operators. The following
example demonstrates the disabling of the addition '+' arithmetic operator:
parser_t parser;
expression_t expression;
parser.settings()
.disable_arithmetic_operation(settings_t::e_arith_add);
parser
.compile("1 + 2 / 3",expression); // failure
parser.settings()
.enable_arithmetic_operation(settings_t::e_arith_add);
parser
.compile("1 + 2 / 3",expression); // success
(5) Inequality Operators
The list of available inequality operators is as follows:
<, <=, >, >=, ==, =, != <>
The above mentioned inequality operators can be either enabled or
disabled 'all' at once, as is demonstrated below:
parser_t parser;
expression_t expression;
parser.settings().disable_all_inequality_ops();
parser
.compile("1 < 3",expression); // compilation failure
parser.settings().enable_all_inequality_ops();
parser
.compile("1 < 3",expression); // compilation success
One can also enable or disable specific inequality operators. The following
example demonstrates the disabling of the less-than '<' inequality operator:
parser_t parser;
expression_t expression;
parser.settings()
.disable_inequality_operation(settings_t::e_ineq_lt);
parser
.compile("1 < 3",expression); // failure
parser.settings()
.enable_inequality_operation(settings_t::e_ineq_lt);
parser
.compile("1 < 3",expression); // success
(6) Assignment Operators
The list of available assignment operators is as follows:
:=, +=, -=, *=, /=, %=
The above mentioned assignment operators can be either enabled or
disabled 'all' at once, as is demonstrated below:
parser_t parser;
expression_t expression;
symbol_table_t symbol_table;
T x = T(0);
symbol_table.add_variable("x",x);
expression.register_symbol_table(symbol_table);
parser.settings().disable_all_assignment_ops();
parser
.compile("x := 3",expression); // compilation failure
parser.settings().enable_all_assignment_ops();
parser
.compile("x := 3",expression); // compilation success
One can also enable or disable specific assignment operators. The following
example demonstrates the disabling of the '+=' addition assignment operator:
parser_t parser;
expression_t expression;
symbol_table_t symbol_table;
T x = T(0);
symbol_table.add_variable("x",x);
expression.register_symbol_table(symbol_table);
parser.settings()
.disable_assignment_operation(settings_t::e_assign_addass);
parser
.compile("x += 3",expression); // failure
parser.settings()
.enable_assignment_operation(settings_t::e_assign_addass);
parser
.compile("x += 3",expression); // success
Note: In the event of a base function being disabled, one can redefine
the base function using the standard custom function definition
process. In the following example the 'sin' function is disabled then
redefined as a function taking degree input.
template <typename T>
struct sine_deg : public exprtk::ifunction<T>
{
sine_deg() : exprtk::ifunction<T>(1) {}
inline T operator()(const T& v)
{
const T pi = exprtk::details::numeric::constant::pi;
return std::sin((v * T(pi)) / T(180));
}
};
.
.
.
typedef exprtk::symbol_table<T> symbol_table_t;
typedef exprtk::expression<T> expression_t;
typedef exprtk::parser<T> parser_t;
typedef typename parser_t::settings_store settings_t;
sine_deg<T> sine;
symbol_table.add_reserved_function("sin",sine);
expression_t expression;
expression.register_symbol_table(symbol_table);
parser_t parser;
parser.settings()
.disable_base_function(settings_t::e_bf_sin);
parser.compile("1 + sin(30)",expression);
In the example above, the custom 'sin' function is registered with the
symbol_table using the method 'add_reserved_function'. This is done so
as to bypass the checks for reserved words that are carried out on the
provided symbol names when calling the standard 'add_function' method.
Normally if a user specified symbol name conflicts with any of the
ExprTk reserved words, the add_function call will fail.
[18 - EXPRESSION RETURN VALUES]
ExprTk expressions can return immediately from any point by utilizing
the return call. Furthermore the return call can be used to transfer
out multiple return values from within the expression.
If an expression evaluation exits using a return point, the result of
the call to the 'value' method will be NaN, and it's expected that the
return values will be available from the results_context.
In the following example there are three return points in the
expression. If neither of the return points are hit, then the
expression will return normally.
std::string expression_string =
" if (x < y) "
" return [x + 1,'return-call 1']; "
" else if (x > y) "
" return [y / 2, y + 1, 'return-call 2']; "
" else if (equal(x,y)) "
" x + y; "
" return [x, y, x + y, x - y, 'return-call 3'] ";
typedef exprtk::symbol_table<double> symbol_table_t;
typedef exprtk::expression<double> expression_t;
typedef exprtk::parser<double> parser_t;
symbol_table_t symbol_table;
expression_t expression;
parser_t parser;
double x = 0;
double y = 0;
symbol_table.add_variable("x",x);
symbol_table.add_variable("y",y);
expression.register_symbol_table(symbol_table);
parser.compile(expression_string,expression);
T result = expression.value();
if (expression.results().count())
{
typedef exprtk::results_context<T> results_context_t;
typedef typename results_context_t::type_store_t type_t;
typedef typename type_t::scalar_view scalar_t;
typedef typename type_t::vector_view vector_t;
typedef typename type_t::string_view string_t;
const results_context_t& result = expression.results();
for (std::size_t i = 0; i < results.count(); ++i)
{
type_t t = results[i];
switch (t.type)
{
case type_t::e_scalar : ...
break;
case type_t::e_vector : ...
break;
case type_t::e_string : ...
break;
default : continue;
}
}
Note: Processing of the return results is very similar to that of the
generic function call parameters.
[19 - COMPILATION ERRORS]
When attempting to compile a malformed or otherwise erroneous ExprTk
expression, the compilation process will result in an error, as is
indicated by the 'compile' method returning a false value. A
diagnostic indicating the first error encountered and its cause can be
obtained by invoking the 'error' method, as is demonstrated in the
following example:
if (!parser.compile(expression_string,expression))
{
printf("Error: %s\n", parser.error().c_str());
return false;
}
Any error(s) resulting from a failed compilation will be stored in the
parser instance until the next time a compilation is performed. Before
then errors can be enumerated in the order they occurred by invoking
the 'get_error' method which itself will return a 'parser_error' type.
A parser_error object will contain an error diagnostic, an error mode
(or class), and the character position of the error in the expression
string. The following example demonstrates the enumeration of error(s)
in the event of a failed compilation.
if (!parser.compile(expression_string,expression))
{
for (std::size_t i = 0; i < parser.error_count(); ++i)
{
typedef exprtk::parser_error::type error_t;
error_t error = parser.get_error(i);
printf("Error[%02d] Position: %02d Type: [%14s] Msg: %s\n",
i,
error.token.position,
exprtk::parser_error::to_str(error.mode).c_str(),
error.diagnostic.c_str());
}
return false;
}
For expressions comprised of multiple lines, the error position
provided in the parser_error object can be converted into a pair of
line and column numbers by invoking the 'update_error' function as is
demonstrated by the following example:
if (!parser.compile(program_str,expression))
{
for (std::size_t i = 0; i < parser.error_count(); ++i)
{
typedef exprtk::parser_error::type error_t;
error_t error = parser.get_error(i);
exprtk::parser_error::update_error(error,program_str);
printf("Error[%02d] at line: %d column: %d\n",
i,
error.line_no,
error.column_no);
}
return false;
}
Note: There are five distinct error modes in ExprTk which denote the
class of an error. These classes are as follows:
(a) Syntax
(b) Token
(c) Numeric
(d) Symbol Table
(e) Lexer
(a) Syntax Errors
These are errors related to invalid syntax found within the denoted
expression. Examples are invalid sequences of operators and variables,
incorrect number of parameters to functions, invalid conditional or
loop structures and invalid use of keywords.
eg: 'for := sin(x,y,z) + 2 * equal > until[2 - x,3]'
(b) Token Errors
Errors in this class relate to token level errors detected by one or
more of the following checkers:
(1) Bracket Checker
(2) Numeric Checker
(3) Sequence Checker
(c) Numeric Errors
This class of error is related to conversion of numeric values from
their string form to the underlying numerical type (float, double
etc).
(d) Symbol Table Errors
This is the class of errors related to failures when interacting with
the registered symbol_table instance. Errors such as not being able to
find, within the symbol_table, symbols representing variables or
functions, to being unable to create new variables in the symbol_table
via the 'unknown symbol resolver' mechanism.
[20 - EXPRTK NOTES]
The following is a list of facts and suggestions one may want to take
into account when using ExprTk:
(00) Precision and performance of expression evaluations are the
dominant principles of the ExprTk library.
(01) ExprTk uses a rudimentary imperative programming model with
syntax based on languages such as Pascal and C. Furthermore
ExprTk is an LL(2) type grammar and is processed using a
recursive descent parsing algorithm.
(02) Supported types are float, double, long double and MPFR/GMP.
(03) Standard mathematical operator precedence is applied (BEDMAS).
(04) Results of expressions that are deemed as being 'valid' are to
exist within the set of Real numbers. All other results will be
of the value: Not-A-Number (NaN).
(05) Supported user defined types are numeric and string
variables, numeric vectors and functions.
(06) All reserved words, keywords, variable, vector, string and
function names are case-insensitive.
(07) Variable, vector, string variable and function names must begin
with a letter (A-Z or a-z), then can be comprised of any
combination of letters, digits and underscores. (eg: x, var1 or
power_func99)
(08) Expression lengths and sub-expression lists are limited only by
storage capacity.
(09) The life-time of objects registered with or created from a
specific symbol-table must span at least the life-time of the
compiled expressions which utilize objects, such as variables,
of that symbol-table, otherwise the result will be undefined
behavior.
(10) Equal and Nequal are normalised-epsilon equality routines,
which use epsilons of 0.0000000001 and 0.000001 for double and
float types respectively.
(11) All trigonometric functions assume radian input unless stated
otherwise.
(12) Expressions may contain white-space characters such as space,
tabs, new-lines, control-feed et al.
('\n', '\r', '\t', '\b', '\v', '\f')
(13) Strings may be comprised of any combination of letters, digits
special characters including (~!@#$%^&*()[]|=+ ,./?<>;:"`~_) or
hexadecimal escaped sequences (eg: \0x30) and must be enclosed
with single-quotes.
eg: 'Frankly my dear, \0x49 do n0t give a damn!'
(14) User defined normal functions can have up to 20 parameters,
where as user defined generic-functions and vararg-functions
can have an unlimited number of parameters.
(15) The inbuilt polynomial functions can be at most of degree 12.
(16) Where appropriate constant folding optimisations may be applied.
(eg: The expression '2 + (3 - (x / y))' becomes '5 - (x / y)')
(17) If the strength reduction compilation option has been enabled,
then where applicable strength reduction optimisations may be
applied.
(18) String processing capabilities are available by default. To
turn them off, the following needs to be defined at compile
time: exprtk_disable_string_capabilities
(19) Composited functions can call themselves or any other functions
that have been defined prior to their own definition.
(20) Recursive calls made from within composited functions will have
a stack size bound by the stack of the executing architecture.
(21) User defined functions by default are assumed to have side
effects. As such an "all constant parameter" invocation of such
functions wont result in constant folding. If the function has
no side effects then that can be noted during the constructor
of the ifunction allowing it to be constant folded where
appropriate.
(22) The entity relationship between symbol_table and an expression
is many-to-many. However the intended 'typical' use-case where
possible, is to have a single symbol table manage the variable
and function requirements of multiple expressions.
(23) The common use-case for an expression is to have it compiled
only ONCE and then subsequently have it evaluated multiple
times. An extremely inefficient and suboptimal approach would
be to recompile an expression from its string form every time
it requires evaluating.
(24) It is strongly recommended that the return value of method
invocations from the parser and symbol_table types be taken
into account. Specifically the 'compile' method of the parser
and the 'add_xxx' set of methods of the symbol_table as they
denote either the success or failure state of the invoked call.
Continued processing from a failed state without having first
rectified the underlying issue will in turn result in further
failures and undefined behaviours.
(25) The following are examples of compliant floating point value
representations:
(1) 12345 (5) -123.456
(2) +123.456e+12 (6) 123.456E-12
(3) +012.045e+07 (7) .1234
(4) 123.456f (8) -321.654E+3L
(26) Expressions may contain any of the following comment styles:
(1) // .... \n
(2) # .... \n
(3) /* .... */
(27) The 'null' value type is a special non-zero type that
incorporates specific semantics when undergoing operations with
the standard numeric type. The following is a list of type and
boolean results associated with the use of 'null':
(1) null +,-,*,/,% x --> x
(2) x +,-,*,/,% null --> x
(3) null +,-,*,/,% null --> null
(4) null == null --> true
(5) null == x --> true
(6) x == null --> true
(7) x != null --> false
(8) null != null --> false
(9) null != x --> false
(28) The following is a list of reserved words and symbols used by
ExprTk. Attempting to add a variable or custom function to a
symbol table using any of the reserved words will result in a
failure.
abs, acos, acosh, and, asin, asinh, atan, atan2, atanh, avg,
break, case, ceil, clamp, continue, cosh, cos, cot, csc,
default, deg2grad, deg2rad, else, equal, erfc, erf, exp,
expm1, false, floor, for, frac, grad2deg, hypot, iclamp, if,
ilike, in, inrange, in, like, log, log10, log1p, log2, logn,
mand, max, min, mod, mor, mul, nand, ncdf, nor, not,
not_equal, not, null, or, pow, rad2deg, repeat, return,
root, roundn, round, sec, sgn, shl, shr, sinc, sinh, sin,
sqrt, sum, swap, switch, tanh, tan, true, trunc, until, var,
while, xnor, xor, xor
(29) Every valid ExprTk statement is a "value returning" expression.
Unlike some languages that limit the types of expressions that
can be performed in certain situations, in ExprTk any valid
expression can be used in any "value consuming" context. eg:
var y := 3;
for (var x := switch
{
case 1 : 7;
case 2 : -1 + ~{var x{};};
default : y > 2 ? 3 : 4;
};
x != while (y > 0) { y -= 1; };
x -= {
if(min(x,y) < 2 * max(x,y))
x + 2;
else
x + y - 3;
}
)
{
(x + y) / (x - y);
}
[21 - SIMPLE EXPRTK EXAMPLE]
--- snip ---
#include <cstdio>
#include <string>
#include "exprtk.hpp"
template <typename T>
struct myfunc : public exprtk::ifunction<T>
{
myfunc() : exprtk::ifunction<T>(2) {}
T operator()(const T& v1, const T& v2)
{
return T(1) + (v1 * v2) / T(3);
}
};
int main()
{
typedef exprtk::symbol_table<double> symbol_table_t;
typedef exprtk::expression<double> expression_t;
typedef exprtk::parser<double> parser_t;
typedef exprtk::parser_error::type error_t;
std::string expression_str =
"z := 2 myfunc([4 + sin(x / pi)^3],y ^ 2)";
double x = 1.1;
double y = 2.2;
double z = 3.3;
myfunc<double> mf;
symbol_table_t symbol_table;
symbol_table.add_constants();
symbol_table.add_variable("x",x);
symbol_table.add_variable("y",y);
symbol_table.add_variable("z",z);
symbol_table.add_function("myfunc",mf);
expression_t expression;
expression.register_symbol_table(symbol_table);
parser_t parser;
if (!parser.compile(expression_str,expression))
{
// A compilation error has occurred. Attempt to
// print all errors to stdout.
printf("Error: %s\tExpression: %s\n",
parser.error().c_str(),
expression_str.c_str());
for (std::size_t i = 0; i < parser.error_count(); ++i)
{
// Include the specific nature of each error
// and its position in the expression string.
error_t error = parser.get_error(i);
printf("Error: %02d Position: %02d "
"Type: [%s] "
"Message: %s "
"Expression: %s\n",
static_cast<int>(i),
static_cast<int>(error.token.position),
exprtk::parser_error::to_str(error.mode).c_str(),
error.diagnostic.c_str(),
expression_str.c_str());
}
return 1;
}
// Evaluate the expression and obtain its result.
double result = expression.value();
printf("Result: %10.5f\n",result);
return 0;
}
--- snip ---
[22 - BUILD OPTIONS]
When building ExprTk there are a number of defines that will enable or
disable certain features and capabilities. The defines can either be
part of a compiler command line switch or scoped around the include to
the ExprTk header. The defines are as follows:
(1) exprtk_enable_debugging
(2) exprtk_disable_comments
(3) exprtk_disable_break_continue
(4) exprtk_disable_sc_andor
(5) exprtk_disable_enhanced_features
(6) exprtk_disable_string_capabilities
(1) exprtk_enable_debugging
This define will enable printing of debug information to stdout during
the compilation process.
(2) exprtk_disable_comments
This define will disable the ability for expressions to have comments.
Expressions that have comments when parsed with a build that has this
option, will result in a compilation failure.
(3) exprtk_disable_break_continue
This define will disable the loop-wise 'break' and 'continue'
capabilities. Any expression that contains those keywords will result
in a compilation failure.
(4) exprtk_disable_sc_andor
This define will disable the short-circuit '&' (and) and '|' (or)
operators
(5) exprtk_disable_enhanced_features
This define will disable all enhanced features such as strength
reduction and special function optimisations and expression specific
type instantiations. This feature will reduce compilation times and
binary sizes but will also result in massive performance degradation
of expression evaluations.
(6) exprtk_disable_string_capabilities
This define will disable all string processing capabilities. Any
expression that contains a string or string related syntax will result
in a compilation failure.
[23 - FILES]
The source distribution of ExprTk is comprised of the following set of
files:
(00) Makefile
(01) readme.txt
(02) exprtk.hpp
(03) exprtk_test.cpp
(04) exprtk_benchmark.cpp
(05) exprtk_simple_example_01.cpp
(06) exprtk_simple_example_02.cpp
(07) exprtk_simple_example_03.cpp
(08) exprtk_simple_example_04.cpp
(09) exprtk_simple_example_05.cpp
(10) exprtk_simple_example_06.cpp
(11) exprtk_simple_example_07.cpp
(12) exprtk_simple_example_08.cpp
(13) exprtk_simple_example_09.cpp
(14) exprtk_simple_example_10.cpp
(15) exprtk_simple_example_11.cpp
(16) exprtk_simple_example_12.cpp
(17) exprtk_simple_example_13.cpp
(18) exprtk_simple_example_14.cpp
(19) exprtk_simple_example_15.cpp
(20) exprtk_simple_example_16.cpp
[24 - LANGUAGE STRUCTURE]
+-------------------------------------------------------------+
|00 - If Statement |
| |
| [if] ---> [(] ---> [condition] -+-> [,] -+ |
| | | |
| +---------------<---------------+ | |
| | | |
| | +------------------<------------------+ |
| | | |
| | +--> [consequent] ---> [,] ---> [alternative] ---> [)] |
| | |
| +--> [)] --+-> [{] ---> [expression*] ---> [}] --+ |
| | | |
| | +---------<----------+ |
| +----<-----+ | |
| | v |
| +--> [consequent] --> [;] -{*}-> [else-statement] |
| |
+-------------------------------------------------------------+
|01 - Else Statement |
| |
| [else] -+-> [alternative] ---> [;] |
| | |
| +--> [{] ---> [expression*] ---> [}] |
| | |
| +--> [if-statement] |
| |
+-------------------------------------------------------------+
|02 - Ternary Statement |
| |
| [condition] ---> [?] ---> [consequent] ---> [:] --+ |
| | |
| +------------------------<------------------------+ |
| | |
| +--> [alternative] --> [;] |
| |
+-------------------------------------------------------------+
|03 - While Loop |
| |
| [while] ---> [(] ---> [condition] ---> [)] ---+ |
| | |
| +----------------------<----------------------+ |
| | |
| +--> [{] ---> [expression*] ---> [}] |
| |
+-------------------------------------------------------------+
|04 - Repeat Until Loop |
| |
| [repeat] ---> [expression*] ---+ |
| | |
| +--------------<---------------+ |
| | |
| +--> [until] ---> [(] ---> [condition] --->[)] |
| |
+-------------------------------------------------------------+
|05 - For Loop |
| |
| [for] ---> [(] -+-> [initialise expression] --+--+ |
| | | | |
| +------------->---------------+ v |
| | |
| +-----------------------<------------------------+ |
| | |
| +--> [;] -+-> [condition] -+-> [;] ---+ |
| | | | |
| +------->--------+ v |
| | |
| +------------------<---------+--------+ |
| | | |
| +--> [increment expression] -+-> [)] --+ |
| | |
| +------------------<-------------------+ |
| | |
| +--> [{] ---> [expression*] ---> [}] |
| |
+-------------------------------------------------------------+
|06 - Switch Statement |
| |
| [switch] ---> [{] ---+ |
| | |
| +---------<----------+-----------<-----------+ |
| | | |
| +--> [case] ---> [condition] ---> [:] ---+ | |
| | | |
| +-------------------<--------------------+ | |
| | | |
| +--> [consequent] ---> [;] --------->--------+ |
| | | |
| | | |
| +--> [default] ---> [consequent] ---> [;] ---+ |
| | | |
| +---------------------<----------------------+ |
| | |
| +--> [}] |
| |
+-------------------------------------------------------------+
|07 - Multi Subexpression Statement |
| |
| +--------------<---------------+ |
| | | |
| [~] ---> [{\(] -+-> [expression] -+-> [;\,] ---+ |
| | |
| +----------------<----------------+ |
| | |
| +--> [}\)] |
| |
+-------------------------------------------------------------+
|08 - Multi Case-Consequent Statement |
| |
| [[*]] ---> [{] ---+ |
| | |
| +--------<--------+--------------<----------+ |
| | | |
| +--> [case] ---> [condition] ---> [:] ---+ | |
| | | |
| +-------------------<--------------------+ | |
| | | |
| +--> [consequent] ---> [;] ---+------>------+ |
| | |
| +--> [}] |
| |
+-------------------------------------------------------------+
|09 - Variable Definition Statement |
| |
| [var] ---> [symbol] -+-> [:=] -+-> [expression] -+-> [;] |
| | | | |
| | +-----> [{}] -->--+ |
| | | |
| +------------->-------------+ |
| |
+-------------------------------------------------------------+
|10 - Vector Definition Statement |
| |
| [var] ---> [symbol] ---> [[] ---> [constant] ---> []] --+ |
| | |
| +---------------------------<---------------------------+ |
| | |
| | +--------->---------+ |
| | | | |
| +--> [:=] ---> [{] -+-+-> [expression] -+-> [}] ---> [;] |
| | | |
| +--<--- [,] <-----+ |
| |
+-------------------------------------------------------------+
|11 - String Definition Statement |
| |
| [var] --> [symbol] --> [:=] --> [str-expression] ---> [;] |
| |
+-------------------------------------------------------------+
|12 - Range Statement |
| |
| +-------->--------+ |
| | | |
| [[] -+-> [expression] -+-> [:] -+-> [expression] -+--> []] |
| | | |
| +-------->--------+ |
| |
+-------------------------------------------------------------+
|13 - Return Statement |
| |
| [return] ---> [[] -+-> [expression] -+-> []] ---> [;] |
| | | |
| +--<--- [,] <-----+ |
| |
+-------------------------------------------------------------+
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