69 lines
2.7 KiB
C
69 lines
2.7 KiB
C
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#include "tommath_private.h"
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#ifdef 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 = MP_MIN(a->used, b->used),
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max = MP_MAX(a->used, b->used),
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digs = a->used + b->used + 1;
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bool neg = (a->sign != b->sign);
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if ((a == b) &&
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MP_HAS(S_MP_SQR_TOOM) && /* use Toom-Cook? */
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(a->used >= MP_SQR_TOOM_CUTOFF)) {
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err = s_mp_sqr_toom(a, c);
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} else if ((a == b) &&
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MP_HAS(S_MP_SQR_KARATSUBA) && /* Karatsuba? */
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(a->used >= MP_SQR_KARATSUBA_CUTOFF)) {
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err = s_mp_sqr_karatsuba(a, c);
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} else if ((a == b) &&
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MP_HAS(S_MP_SQR_COMBA) && /* can we use the fast comba multiplier? */
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(((a->used * 2) + 1) < MP_WARRAY) &&
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(a->used < (MP_MAX_COMBA / 2))) {
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err = s_mp_sqr_comba(a, c);
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} else if ((a == b) &&
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MP_HAS(S_MP_SQR)) {
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err = s_mp_sqr(a, c);
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} else if (MP_HAS(S_MP_MUL_BALANCE) &&
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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_MUL_KARATSUBA_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 s_mp_mul_comba
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* was actually slower on the author's machine, but YMMV.
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*/
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(min >= MP_MUL_KARATSUBA_CUTOFF) &&
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((max / 2) >= MP_MUL_KARATSUBA_CUTOFF) &&
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/* Not much effect was observed below a ratio of 1:2, but again: YMMV. */
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(max >= (2 * min))) {
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err = s_mp_mul_balance(a,b,c);
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} else if (MP_HAS(S_MP_MUL_TOOM) &&
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(min >= MP_MUL_TOOM_CUTOFF)) {
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err = s_mp_mul_toom(a, b, c);
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} else if (MP_HAS(S_MP_MUL_KARATSUBA) &&
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(min >= MP_MUL_KARATSUBA_CUTOFF)) {
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err = s_mp_mul_karatsuba(a, b, c);
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} else if (MP_HAS(S_MP_MUL_COMBA) &&
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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 <= MP_MAX_COMBA)) {
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err = s_mp_mul_comba(a, b, c, digs);
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} else if (MP_HAS(S_MP_MUL)) {
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err = s_mp_mul(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_NEG : MP_ZPOS;
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return err;
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}
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#endif
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