#include "tommath_private.h"
#ifdef MP_MUL_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */
/* high level multiplication (handles sign) */
mp_err mp_mul(const mp_int *a, const mp_int *b, mp_int *c)
{
mp_err err;
int min_len = MP_MIN(a->used, b->used),
max_len = MP_MAX(a->used, b->used),
digs = a->used + b->used + 1;
mp_sign neg = (a->sign == b->sign) ? MP_ZPOS : MP_NEG;
if (MP_HAS(S_MP_BALANCE_MUL) &&
/* Check sizes. The smaller one needs to be larger than the Karatsuba cut-off.
* The bigger one needs to be at least about one MP_KARATSUBA_MUL_CUTOFF bigger
* to make some sense, but it depends on architecture, OS, position of the
* stars... so YMMV.
* Using it to cut the input into slices small enough for s_mp_mul_digs_fast
* was actually slower on the author's machine, but YMMV.
*/
(min_len >= MP_KARATSUBA_MUL_CUTOFF) &&
((max_len / 2) >= MP_KARATSUBA_MUL_CUTOFF) &&
/* Not much effect was observed below a ratio of 1:2, but again: YMMV. */
(max_len >= (2 * min_len))) {
err = s_mp_balance_mul(a,b,c);
} else if (MP_HAS(S_MP_TOOM_MUL) &&
(min_len >= MP_TOOM_MUL_CUTOFF)) {
err = s_mp_toom_mul(a, b, c);
} else if (MP_HAS(S_MP_KARATSUBA_MUL) &&
(min_len >= MP_KARATSUBA_MUL_CUTOFF)) {
err = s_mp_karatsuba_mul(a, b, c);
} else if (MP_HAS(S_MP_MUL_DIGS_FAST) &&
/* can we use the fast multiplier?
*
* The fast multiplier can be used if the output will
* have less than MP_WARRAY digits and the number of
* digits won't affect carry propagation
*/
(digs < MP_WARRAY) &&
(min_len <= MP_MAXFAST)) {
err = s_mp_mul_digs_fast(a, b, c, digs);
} else if (MP_HAS(S_MP_MUL_DIGS)) {
err = s_mp_mul_digs(a, b, c, digs);
} else {
err = MP_VAL;
}
c->sign = (c->used > 0) ? neg : MP_ZPOS;
return err;
}
#endif
