#include "tommath_private.h"
#ifdef BN_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;
mp_sign neg;
#ifdef BN_S_MP_BALANCE_MUL_C
int len_b, len_a;
#endif
neg = (a->sign == b->sign) ? MP_ZPOS : MP_NEG;
#ifdef BN_S_MP_BALANCE_MUL_C
len_a = a->used;
len_b = b->used;
if (len_a == len_b) {
goto GO_ON;
}
/*
* Check sizes. The smaller one needs to be larger than the Karatsuba cut-off.
* The bigger one needs to be at least about one 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 fast_s_mp_mul_digs
* was actually slower on the author's machine, but YMMV.
*/
if ((MP_MIN(len_a, len_b) < MP_KARATSUBA_MUL_CUTOFF)
|| ((MP_MAX(len_a, len_b) / 2) < MP_KARATSUBA_MUL_CUTOFF)) {
goto GO_ON;
}
/*
* Not much effect was observed below a ratio of 1:2, but again: YMMV.
*/
if ((MP_MAX(len_a, len_b) / MP_MIN(len_a, len_b)) < 2) {
goto GO_ON;
}
err = s_mp_balance_mul(a,b,c);
goto END;
GO_ON:
#endif
/* use Toom-Cook? */
#ifdef BN_S_MP_TOOM_MUL_C
if (MP_MIN(a->used, b->used) >= MP_TOOM_MUL_CUTOFF) {
err = s_mp_toom_mul(a, b, c);
} else
#endif
#ifdef BN_S_MP_KARATSUBA_MUL_C
/* use Karatsuba? */
if (MP_MIN(a->used, b->used) >= MP_KARATSUBA_MUL_CUTOFF) {
err = s_mp_karatsuba_mul(a, b, c);
} else
#endif
{
/* 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
*/
int digs = a->used + b->used + 1;
#ifdef BN_S_MP_MUL_DIGS_FAST_C
if ((digs < MP_WARRAY) &&
(MP_MIN(a->used, b->used) <= MP_MAXFAST)) {
err = s_mp_mul_digs_fast(a, b, c, digs);
} else
#endif
{
#ifdef BN_S_MP_MUL_DIGS_C
err = s_mp_mul_digs(a, b, c, a->used + b->used + 1);
#else
err = MP_VAL;
#endif
}
}
END:
c->sign = (c->used > 0) ? neg : MP_ZPOS;
return err;
}
#endif