kc3-lang/libtommath/bn_mp_balance_mul.c

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• Hash : 27ca25cb
  Author :
  Date : 2019-04-06T18:55:43
  

  added multiplcation balancing for the Toom-Cook algorithms

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• bn_mp_balance_mul.c

• #include "tommath_private.h"
  #ifdef BN_MP_BALANCE_MUL_C
  /* LibTomMath, multiple-precision integer library -- Tom St Denis */
  /* SPDX-License-Identifier: Unlicense */
  
  /* single-digit multiplication with the smaller number as the single-digit */
  int mp_balance_mul(const mp_int *a, const mp_int *b, mp_int *c)
  {
     int e, count, len_a, len_b, nblocks, i, j, bsize;
     mp_int a0, tmp, A, B, r;
  
     len_a = a->used;
     len_b = b->used;
  
     nblocks = MAX(a->used, b->used) / MIN(a->used, b->used);
     bsize = MIN(a->used, b->used) ;
     e = MP_OKAY;
  
     if ((e = mp_init_size(&a0, bsize + 2)) != MP_OKAY) {
        return e;
     }
     if ((e = mp_init_multi(&tmp, &r, NULL)) != MP_OKAY) {
        mp_clear(&a0);
        return e;
     }
  
     /* Make sure that A is the larger one*/
     if (len_a < len_b) {
        B = *a;
        A = *b;
     } else {
        A = *a;
        B = *b;
     }
  
     for (i = 0, j=0; i < nblocks; i++) {
        /* Cut a slice off of a */
        a0.used = 0;
        for (count = 0; count < bsize; count++) {
           a0.dp[count] = A.dp[ j++ ];
           a0.used++;
        }
        /* Multiply with b */
        if ((e = mp_mul(&a0, &B, &tmp)) != MP_OKAY) {
           goto LBL_ERR;
        }
        /* Shift tmp to the correct position */
        if ((e = mp_lshd(&tmp, bsize * i)) != MP_OKAY) {
           goto LBL_ERR;
        }
        /* Add to output. No carry needed */
        if ((e = mp_add(&r, &tmp, &r)) != MP_OKAY) {
           goto LBL_ERR;
        }
     }
     /* The left-overs; there are always left-overs */
     if (j < A.used) {
        a0.used = 0;
        for (count = 0; j < A.used; count++) {
           a0.dp[count] = A.dp[ j++ ];
           a0.used++;
        }
        if ((e = mp_mul(&a0, &B, &tmp)) != MP_OKAY) {
           goto LBL_ERR;
        }
        if ((e = mp_lshd(&tmp, bsize * i)) != MP_OKAY) {
           goto LBL_ERR;
        }
        if ((e = mp_add(&r, &tmp, &r)) != MP_OKAY) {
           goto LBL_ERR;
        }
     }
  
     mp_exch(&r,c);
  LBL_ERR:
     mp_clear_multi(&a0, &tmp, &r,NULL);
     return e;
  }
  #endif
  

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