54 lines
2.4 KiB
C
54 lines
2.4 KiB
C
#include "amplify_tommath_private.h"
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#ifdef AMPLIFY_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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/* Modifications Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved. */
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/* high level multiplication (handles sign) */
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amplify_mp_err amplify_mp_mul(const amplify_mp_int *a, const amplify_mp_int *b, amplify_mp_int *c)
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{
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amplify_mp_err err;
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int min_len = AMPLIFY_MP_MIN(a->used, b->used),
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max_len = AMPLIFY_MP_MAX(a->used, b->used),
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digs = a->used + b->used + 1;
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amplify_mp_sign neg = (a->sign == b->sign) ? AMPLIFY_MP_ZPOS : AMPLIFY_MP_NEG;
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if (AMPLIFY_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 AMPLIFY_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 amplify_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 >= AMPLIFY_MP_KARATSUBA_MUL_CUTOFF) &&
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((max_len / 2) >= AMPLIFY_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_amplify_mp_balance_mul(a,b,c);
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} else if (AMPLIFY_MP_HAS(S_MP_TOOM_MUL) &&
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(min_len >= AMPLIFY_MP_TOOM_MUL_CUTOFF)) {
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err = amplify_s_mp_toom_mul(a, b, c);
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} else if (AMPLIFY_MP_HAS(S_MP_KARATSUBA_MUL) &&
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(min_len >= AMPLIFY_MP_KARATSUBA_MUL_CUTOFF)) {
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err = amplify_s_mp_karatsuba_mul(a, b, c);
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} else if (AMPLIFY_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 AMPLIFY_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 < AMPLIFY_MP_WARRAY) &&
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(min_len <= AMPLIFY_MP_MAXFAST)) {
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err = amplify_s_mp_mul_digs_fast(a, b, c, digs);
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} else if (AMPLIFY_MP_HAS(S_MP_MUL_DIGS)) {
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err = amplify_s_mp_mul_digs(a, b, c, digs);
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} else {
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err = AMPLIFY_MP_VAL;
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}
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c->sign = (c->used > 0) ? neg : AMPLIFY_MP_ZPOS;
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return err;
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}
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#endif
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