1 #include "tommath_private.h"
3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
4 /* SPDX-License-Identifier: Unlicense */
6 /* high level multiplication (handles sign) */
7 mp_err mp_mul(const mp_int *a, const mp_int *b, mp_int *c)
10 int min_len = MP_MIN(a->used, b->used),
11 max_len = MP_MAX(a->used, b->used),
12 digs = a->used + b->used + 1;
13 mp_sign neg = (a->sign == b->sign) ? MP_ZPOS : MP_NEG;
15 if (MP_HAS(S_MP_BALANCE_MUL) &&
16 /* Check sizes. The smaller one needs to be larger than the Karatsuba cut-off.
17 * The bigger one needs to be at least about one MP_KARATSUBA_MUL_CUTOFF bigger
18 * to make some sense, but it depends on architecture, OS, position of the
20 * Using it to cut the input into slices small enough for fast_s_mp_mul_digs
21 * was actually slower on the author's machine, but YMMV.
23 (min_len >= MP_KARATSUBA_MUL_CUTOFF) &&
24 ((max_len / 2) >= MP_KARATSUBA_MUL_CUTOFF) &&
25 /* Not much effect was observed below a ratio of 1:2, but again: YMMV. */
26 (max_len >= (2 * min_len))) {
27 err = s_mp_balance_mul(a,b,c);
28 } else if (MP_HAS(S_MP_TOOM_MUL) &&
29 (min_len >= MP_TOOM_MUL_CUTOFF)) {
30 err = s_mp_toom_mul(a, b, c);
31 } else if (MP_HAS(S_MP_KARATSUBA_MUL) &&
32 (min_len >= MP_KARATSUBA_MUL_CUTOFF)) {
33 err = s_mp_karatsuba_mul(a, b, c);
34 } else if (MP_HAS(S_MP_MUL_DIGS_FAST) &&
35 /* can we use the fast multiplier?
37 * The fast multiplier can be used if the output will
38 * have less than MP_WARRAY digits and the number of
39 * digits won't affect carry propagation
42 (min_len <= MP_MAXFAST)) {
43 err = s_mp_mul_digs_fast(a, b, c, digs);
44 } else if (MP_HAS(S_MP_MUL_DIGS)) {
45 err = s_mp_mul_digs(a, b, c, digs);
49 c->sign = (c->used > 0) ? neg : MP_ZPOS;