88 lines
2.4 KiB
C
88 lines
2.4 KiB
C
#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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int mp_mul(const mp_int *a, const mp_int *b, mp_int *c)
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{
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int res, neg;
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#ifdef BN_MP_BALANCE_MUL_C
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int len_b, len_a;
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#endif
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neg = (a->sign == b->sign) ? MP_ZPOS : MP_NEG;
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#ifdef BN_MP_BALANCE_MUL_C
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len_a = a->used;
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len_b = b->used;
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if (len_a == len_b) {
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goto GO_ON;
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}
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/*
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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 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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if ((MP_MIN(len_a, len_b) < KARATSUBA_MUL_CUTOFF)
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|| ((MP_MAX(len_a, len_b) / 2) < KARATSUBA_MUL_CUTOFF)) {
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goto GO_ON;
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}
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/*
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* Not much effect was observed below a ratio of 1:2, but again: YMMV.
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*/
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if ((MP_MAX(len_a, len_b) / MP_MIN(len_a, len_b)) < 2) {
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goto GO_ON;
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}
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res = mp_balance_mul(a,b,c);
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goto END;
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GO_ON:
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#endif
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/* use Toom-Cook? */
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#ifdef BN_MP_TOOM_MUL_C
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if (MP_MIN(a->used, b->used) >= TOOM_MUL_CUTOFF) {
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res = mp_toom_mul(a, b, c);
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} else
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#endif
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#ifdef BN_MP_KARATSUBA_MUL_C
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/* use Karatsuba? */
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if (MP_MIN(a->used, b->used) >= KARATSUBA_MUL_CUTOFF) {
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res = mp_karatsuba_mul(a, b, c);
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} else
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#endif
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{
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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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int digs = a->used + b->used + 1;
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#ifdef BN_FAST_S_MP_MUL_DIGS_C
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if ((digs < (int)MP_WARRAY) &&
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(MP_MIN(a->used, b->used) <=
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(int)(1u << ((CHAR_BIT * sizeof(mp_word)) - (2u * (size_t)DIGIT_BIT))))) {
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res = fast_s_mp_mul_digs(a, b, c, digs);
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} else
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#endif
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{
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#ifdef BN_S_MP_MUL_DIGS_C
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res = s_mp_mul(a, b, c); /* uses s_mp_mul_digs */
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#else
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res = MP_VAL;
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#endif
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}
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}
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END:
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c->sign = (c->used > 0) ? neg : MP_ZPOS;
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return res;
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}
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#endif
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