Starting in late 2016 we began refactoring and improving the code organization of imath somewhat. Since then our repo has diverged with the upstream repo, but also the divergence is mostly in code formatting and doc changes upstream has continued to pursue. Overall, imath is feature complete and functioning as needed, but this branch has nicer code organization for us to manage inside our own projects.

We appreciate using imath for its ability to be compiled standalone with no dependencies required and is still highly performing compared to other simple-to-build bignum libraries.

Arbitrary precision integer and rational arithmetic library.

IMath is an open-source ANSI C arbitrary precision integer and rational arithmetic library.

IMath is copyright © 2002-2009 Michael J. Fromberger.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

IMath is a library written in portable ANSI C that allows you to perform arithmetic on integers and rational numbers of arbitrary precision. While many programming languages, including Java, Perl, and Python provide arbitrary precision numbers as a standard library or language feature, C does not.

IMath was designed to be small, self-contained, easy to understand and use, and as portable as possible across various platforms. The API is simple, and the code should be comparatively easy to modify or extend. Simplicity and portability are useful goals for some applications—however, IMath does not attempt to break performance records. If you need the fastest possible implementation, you might consider some other libraries, such as GNU MP (GMP), MIRACL, or the bignum library from OpenSSL.

Detailed descriptions of the IMath API can be found in doc.txt. However, the following is a brief synopsis of how to get started with some simple tasks.

To do basic integer arithmetic, you must declare variables of type mpz_t in your program, and call the functions defined in imath.h to operate on them. Here is a simple example that reads one base-10 integer from the command line, multiplies it by another (fixed) value, and prints the result to the standard output in base-10 notation:

#include <stdio.h>
#include <stdlib.h>
#include "imath.h"

int main(int argc, char *argv[])
{
  mpz_t  a, b;
  char  *buf;
  int    len;

  if(argc < 2) {
    fprintf(stderr, "Usage: testprogram <integer>\n");
    return 1;
  }

  /* Initialize a new zero-valued mpz_t structure */
  mp_int_init(&a);

  /* Initialize a new mpz_t with a small integer value */
  mp_int_init_value(&b, 25101);

  /* Read a string value in the specified radix */
  mp_int_read_string(&a, 10, argv[1]);

  /* Multiply the two together... */
  mp_int_mul(&a, &b, &a);

  /* Print out the result */
  len = mp_int_string_len(&a, 10);
  buf = calloc(len, sizeof(*buf));
  mp_int_to_string(&a, 10, buf, len);
  printf("result = %s\n", buf);
  free(buf);

  /* Release memory occupied by mpz_t structures when finished */
  mp_int_clear(&b);
  mp_int_clear(&a);

  return 0;
}

This simple example program does not do any error checking, but all the IMath API functions return an mp_result value which can be used to detect various problems like range errors, running out of memory, and undefined results.

The IMath API also supports operations on arbitrary precision rational numbers. The functions for creating and manipulating rational values (type mpq_t) are defined in imrat.h, so that you need only include them in your project if you wish to.