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About IMath

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.

Programming with IMath

Detailed descriptions of the IMath API can be found in doc.md. 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.