kc3-lang/libtommath/mp_reduce_2k_l.c

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• Hash : 56144eed
  Author :
  Date : 2019-10-29T20:08:42
  

  simplifications: reduce functions

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• mp_reduce_2k_l.c

• #include "tommath_private.h"
  #ifdef MP_REDUCE_2K_L_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
     This differs from reduce_2k since "d" can be larger
     than a single digit.
  */
  mp_err mp_reduce_2k_l(mp_int *a, const mp_int *n, const mp_int *d)
  {
     mp_int q;
     mp_err err;
     int    p;
  
     if ((err = mp_init(&q)) != MP_OKAY) {
        return err;
     }
  
     p = mp_count_bits(n);
  
     for (;;) {
        /* q = a/2**p, a = a mod 2**p */
        if ((err = mp_div_2d(a, p, &q, a)) != MP_OKAY) {
           goto LBL_ERR;
        }
  
        /* q = q * d */
        if ((err = mp_mul(&q, d, &q)) != MP_OKAY) {
           goto LBL_ERR;
        }
  
        /* a = a + q */
        if ((err = s_mp_add(a, &q, a)) != MP_OKAY) {
           goto LBL_ERR;
        }
  
        if (mp_cmp_mag(a, n) == MP_LT) {
           break;
        }
        if ((err = s_mp_sub(a, n, a)) != MP_OKAY) {
           goto LBL_ERR;
        }
  
     }
  
  LBL_ERR:
     mp_clear(&q);
     return err;
  }
  
  #endif
  

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