kc3-lang/libtommath/bn_mp_reduce_2k.c

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• Hash : ff561404
  Author :
  Date : 2019-04-07T15:29:11
  

  shorter headers

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• bn_mp_reduce_2k.c

• #include "tommath_private.h"
  #ifdef BN_MP_REDUCE_2K_C
  /* LibTomMath, multiple-precision integer library -- Tom St Denis */
  /* SPDX-License-Identifier: Unlicense */
  
  /* reduces a modulo n where n is of the form 2**p - d */
  int mp_reduce_2k(mp_int *a, const mp_int *n, mp_digit d)
  {
     mp_int q;
     int    p, res;
  
     if ((res = mp_init(&q)) != MP_OKAY) {
        return res;
     }
  
     p = mp_count_bits(n);
  top:
     /* q = a/2**p, a = a mod 2**p */
     if ((res = mp_div_2d(a, p, &q, a)) != MP_OKAY) {
        goto LBL_ERR;
     }
  
     if (d != 1u) {
        /* q = q * d */
        if ((res = mp_mul_d(&q, d, &q)) != MP_OKAY) {
           goto LBL_ERR;
        }
     }
  
     /* a = a + q */
     if ((res = s_mp_add(a, &q, a)) != MP_OKAY) {
        goto LBL_ERR;
     }
  
     if (mp_cmp_mag(a, n) != MP_LT) {
        if ((res = s_mp_sub(a, n, a)) != MP_OKAY) {
           goto LBL_ERR;
        }
        goto top;
     }
  
  LBL_ERR:
     mp_clear(&q);
     return res;
  }
  
  #endif
  

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