bn_mp_mod_2d.c

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Author : Daniel Mendler
Date : 2019-05-13 00:22:18
Hash : 4534056c
Message : use enums mp_err, mp_ord, mp_bool, mp_sign * MP_USE_ENUMS enables enums * Wc++-compat catches some implicit conversions if MP_USE_ENUMS is defined * 100% backwards compatible API/ABI if MP_USE_ENUMS is not defined

bn_mp_mod_2d.c

#include "tommath_private.h"
#ifdef BN_MP_MOD_2D_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */

/* calc a value mod 2**b */
mp_err mp_mod_2d(const mp_int *a, int b, mp_int *c)
{
   int x;
   mp_err res;

   /* if b is <= 0 then zero the int */
   if (b <= 0) {
      mp_zero(c);
      return MP_OKAY;
   }

   /* if the modulus is larger than the value than return */
   if (b >= (a->used * MP_DIGIT_BIT)) {
      return mp_copy(a, c);
   }

   /* copy */
   if ((res = mp_copy(a, c)) != MP_OKAY) {
      return res;
   }

   /* zero digits above the last digit of the modulus */
   x = (b / MP_DIGIT_BIT) + (((b % MP_DIGIT_BIT) == 0) ? 0 : 1);
   MP_ZERO_DIGITS(c->dp + x, c->used - x);

   /* clear the digit that is not completely outside/inside the modulus */
   c->dp[b / MP_DIGIT_BIT] &=
      ((mp_digit)1 << (mp_digit)(b % MP_DIGIT_BIT)) - (mp_digit)1;
   mp_clamp(c);
   return MP_OKAY;
}
#endif

kc3-lang/libtommath/bn_mp_mod_2d.c

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