oblivia-simplex / crc-tool Goto Github PK

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Olivia Lucca Fraser
October 25, 2015

This is a straightforward implementation of the shift-register
algorithm for computing cyclic redundancy checks on bitstreams.

An automated series of tests can be run using the bash script,
crc-experiment.sh, or the utility can be played with directly.
The utility admits a variety of command line options, which are
detailed in the help menu:

CRC UTILITY
=-=-=-=-=-=
Usage: ./CRC [OPTIONS]
-v: verbose
-q: quiet (diable verbose output)
-f <filename>: supply file as input, instead of stdin
-f - : read from stdin (default)
-s: execute send phase only; append remainder, but do not check
-r: execute receive phase only; check for remainder, but don't append
-b: read input as binary string of ASCII '0's and '1's
-c: read input as raw characters [default]
-o: output bitstring only: use with -b to chain CRC pipes together
-e <burst length>: introduce burst error of <burst length> bits
-g <generator>: supply alternate CRC polynomial in hex or decimal
-h: display this help menu.


Input can be provided as either a stream of raw characters (using
the -c flag, which is also the default setting), or binary notation
(using the -b flag) -- i.e., a series of ASCII '0's and '1's (bytes
0x30 and 0x31, not 0x00 and 0x01). 

A burst error can be introduced using the -e flag, and an integer
argument.

The default generator is 0x04C11DB7, which is commonly used in
CRC-32 applications. Other generators can be substituted for this
one, using the -g flag, and a numerical argument (in either decimal
or hexidecimal notation). 

The -s and -r flags can be used to separate the send and receive
functionality of the CRC programme. This can be useful for performing
CRC calculations as needed (see 3ab.txt for some examples), or
chaining instances of CRC together with Unix pipes.

For example:

$ echo 101101101 | ./CRC -sbog 0xb | ./CRC -rbvg 0xb

MESSAGE READ: m	
IN BINARY:    101101101001
XORPLATE:     11
[01] SHIFTREG: 001  FED: 1  
[02] SHIFTREG: 010  FED: 0  
[03] SHIFTREG: 101  FED: 1  
[04] SHIFTREG: 000  FED: 1  XOR EVENT
[05] SHIFTREG: 000  FED: 0  
[06] SHIFTREG: 001  FED: 1  
[07] SHIFTREG: 011  FED: 1  
[08] SHIFTREG: 110  FED: 0  
[09] SHIFTREG: 110  FED: 1  XOR EVENT
[10] SHIFTREG: 111  FED: 0  XOR EVENT
[11] SHIFTREG: 101  FED: 0  XOR EVENT
[12] SHIFTREG: 000  FED: 1  XOR EVENT
[13] SHIFTREG: 000  FED: 0  
[14] SHIFTREG: 000  FED: 0  
[15] SHIFTREG: 000  FED: 0  
IN:  101101101001
OUT: 101101101001

NO CORRUPTION DETECTED.

This is essentially the same as performing both calculations inside
one instance of CRC with the following command:

$ echo 101101101 | ./CRC -bg 0xb

MESSAGE READ: m
IN BINARY:    101101101
XORPLATE:     11
[01] SHIFTREG: 001  FED: 1  
[02] SHIFTREG: 010  FED: 0  
[03] SHIFTREG: 101  FED: 1  
[04] SHIFTREG: 000  FED: 1  XOR EVENT
[05] SHIFTREG: 000  FED: 0  
[06] SHIFTREG: 001  FED: 1  
[07] SHIFTREG: 011  FED: 1  
[08] SHIFTREG: 110  FED: 0  
[09] SHIFTREG: 110  FED: 1  XOR EVENT
[10] SHIFTREG: 111  FED: 0  XOR EVENT
[11] SHIFTREG: 101  FED: 0  XOR EVENT
[12] SHIFTREG: 001  FED: 0  XOR EVENT
(2) copying 0 from shiftreg to bitmsg_out bit #9
(1) copying 0 from shiftreg to bitmsg_out bit #10
(0) copying 1 from shiftreg to bitmsg_out bit #11
IN:  101101101
OUT: 101101101001

XORPLATE:     11
[01] SHIFTREG: 001  FED: 1  
[02] SHIFTREG: 010  FED: 0  
[03] SHIFTREG: 101  FED: 1  
[04] SHIFTREG: 000  FED: 1  XOR EVENT
[05] SHIFTREG: 000  FED: 0  
[06] SHIFTREG: 001  FED: 1  
[07] SHIFTREG: 011  FED: 1  
[08] SHIFTREG: 110  FED: 0  
[09] SHIFTREG: 110  FED: 1  XOR EVENT
[10] SHIFTREG: 111  FED: 0  XOR EVENT
[11] SHIFTREG: 101  FED: 0  XOR EVENT
[12] SHIFTREG: 000  FED: 1  XOR EVENT
[13] SHIFTREG: 000  FED: 0  
[14] SHIFTREG: 000  FED: 0  
[15] SHIFTREG: 000  FED: 0  
IN:  101101101001
OUT: 101101101001

NO CORRUPTION DETECTED.