tommath/bn_mp_submod.c

#include <tommath_private.h>
#ifdef BN_MP_SUBMOD_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
 */

/* d = a - b (mod c) */
int
mp_submod (mp_int * a, mp_int * b, mp_int * c, mp_int * d)
{
  int     res;
  mp_int  t;


  if ((res = mp_init(&t)) != MP_OKAY) {
    return res;
  }

  if ((res = mp_sub(a, b, &t)) != MP_OKAY) {
    mp_clear(&t);
    return res;
  }
  res = mp_mod(&t, c, d);
  mp_clear(&t);
  return res;
}
#endif

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