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#include "tommath_private.h"
#ifdef BN_S_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 */
mp_err s_mp_balance_mul(const mp_int *a, const mp_int *b, mp_int *c)
{
int count, len_a, len_b, nblocks, i, j, bsize;
mp_int a0, tmp, A, B, r;
mp_err err;
len_a = a->used;
len_b = b->used;
nblocks = MP_MAX(a->used, b->used) / MP_MIN(a->used, b->used);
bsize = MP_MIN(a->used, b->used) ;
if ((err = mp_init_size(&a0, bsize + 2)) != MP_OKAY) {
return err;
}
if ((err = mp_init_multi(&tmp, &r, NULL)) != MP_OKAY) {
mp_clear(&a0);
return err;
}
/* 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++;
}
mp_clamp(&a0);
/* Multiply with b */
if ((err = mp_mul(&a0, &B, &tmp)) != MP_OKAY) {
goto LBL_ERR;
}
/* Shift tmp to the correct position */
if ((err = mp_lshd(&tmp, bsize * i)) != MP_OKAY) {
goto LBL_ERR;
}
/* Add to output. No carry needed */
if ((err = 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++;
}
mp_clamp(&a0);
if ((err = mp_mul(&a0, &B, &tmp)) != MP_OKAY) {
goto LBL_ERR;
}
if ((err = mp_lshd(&tmp, bsize * i)) != MP_OKAY) {
goto LBL_ERR;
}
if ((err = mp_add(&r, &tmp, &r)) != MP_OKAY) {
goto LBL_ERR;
}
}
mp_exch(&r,c);
LBL_ERR:
mp_clear_multi(&a0, &tmp, &r,NULL);
return err;
}
#endif
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