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