bn_mp_mod.c

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Author : Moritz Lenz
Date : 2012-01-08 20:49:01
Hash : 265651b2
Message : Fix mp_mod(a, b, c) if b < 0 and a = n * b, n integer it used to return b, now it return 0.

bn_mp_mod.c

#include <tommath.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, tomstdenis@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 (&t)) != MP_OKAY) {
    return res;
  }

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

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

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

/* $Source$ */
/* $Revision$ */
/* $Date$ */

kc3-lang/libtommath/bn_mp_mod.c

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