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