t8-mod/deps/libtommath/s_mp_mul_balance.c
2024-02-15 15:46:47 -05:00

72 lines
1.8 KiB
C

#include "tommath_private.h"
#ifdef S_MP_MUL_BALANCE_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_mul_balance(const mp_int *a, const mp_int *b, mp_int *c)
{
mp_int a0, tmp, r;
mp_err err;
int i, j,
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 (a->used < b->used) {
MP_EXCH(const mp_int *, a, b);
}
for (i = 0, j=0; i < nblocks; i++) {
/* Cut a slice off of a */
a0.used = bsize;
s_mp_copy_digs(a0.dp, a->dp + j, a0.used);
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 = a->used - j;
s_mp_copy_digs(a0.dp, a->dp + j, a0.used);
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