#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 err;

   /* 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 ((err = mp_copy(a, c)) != MP_OKAY) {

      return err;

   }

   /* 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