1 #include "tommath_private.h"
2 #ifdef BN_MP_MUL_C
3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
4 /* SPDX-License-Identifier: Unlicense */
5
6 /* high level multiplication (handles sign) */
mp_mul(const mp_int * a,const mp_int * b,mp_int * c)7 mp_err mp_mul(const mp_int *a, const mp_int *b, mp_int *c)
8 {
9 mp_err err;
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;
14
15 if (a == b) {
16 return mp_sqr(a,c);
17 } else if (MP_HAS(S_MP_BALANCE_MUL) &&
18 /* Check sizes. The smaller one needs to be larger than the Karatsuba cut-off.
19 * The bigger one needs to be at least about one MP_KARATSUBA_MUL_CUTOFF bigger
20 * to make some sense, but it depends on architecture, OS, position of the
21 * stars... so YMMV.
22 * Using it to cut the input into slices small enough for fast_s_mp_mul_digs
23 * was actually slower on the author's machine, but YMMV.
24 */
25 (min_len >= MP_KARATSUBA_MUL_CUTOFF) &&
26 ((max_len / 2) >= MP_KARATSUBA_MUL_CUTOFF) &&
27 /* Not much effect was observed below a ratio of 1:2, but again: YMMV. */
28 (max_len >= (2 * min_len))) {
29 err = s_mp_balance_mul(a,b,c);
30 } else if (MP_HAS(S_MP_TOOM_MUL) &&
31 (min_len >= MP_TOOM_MUL_CUTOFF)) {
32 err = s_mp_toom_mul(a, b, c);
33 } else if (MP_HAS(S_MP_KARATSUBA_MUL) &&
34 (min_len >= MP_KARATSUBA_MUL_CUTOFF)) {
35 err = s_mp_karatsuba_mul(a, b, c);
36 } else if (MP_HAS(S_MP_MUL_DIGS_FAST) &&
37 /* can we use the fast multiplier?
38 *
39 * The fast multiplier can be used if the output will
40 * have less than MP_WARRAY digits and the number of
41 * digits won't affect carry propagation
42 */
43 (digs < MP_WARRAY) &&
44 (min_len <= MP_MAXFAST)) {
45 err = s_mp_mul_digs_fast(a, b, c, digs);
46 } else if (MP_HAS(S_MP_MUL_DIGS)) {
47 err = s_mp_mul_digs(a, b, c, digs);
48 } else {
49 err = MP_VAL;
50 }
51 c->sign = (c->used > 0) ? neg : MP_ZPOS;
52 return err;
53 }
54 #endif
55