libtommath/bn_mp_mod.c

#include <tommath_private.h>
#ifdef BN_MP_MOD_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis
 *
 * LibTomMath is a library that provides multiple-precision
 * integer arithmetic as well as number theoretic functionality.
 *
 * The library was designed directly after the MPI library by
 * Michael Fromberger but has been written from scratch with
 * additional optimizations in place.
 *
 * The library is free for all purposes without any express
 * guarantee it works.
 *
 * Tom St Denis, tstdenis82@gmail.com, http://libtom.org
 */

/* c = a mod b, 0 <= c < b if b > 0, b < c <= 0 if b < 0 */
int mp_mod(mp_int *a, mp_int *b, mp_int *c)
{
  mp_int  t;
  int     res;

  if ((res = mp_init_size(&t, b->used)) != MP_OKAY) {
    return res;
  }

  if ((res = mp_div(a, b, NULL, &t)) != MP_OKAY) {
    mp_clear(&t);
    return res;
  }

  if ((mp_iszero(&t) != MP_NO) || (t.sign == b->sign)) {
    res = MP_OKAY;
    mp_exch(&t, c);
  } else {
    res = mp_add(b, &t, c);
  }

  mp_clear(&t);
  return res;
}
#endif

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