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annotate libtommath/bn_mp_mul.c @ 1820:e9854650d45b

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Clarify help text for dropbear -e environment option
author Matt Johnston <matt@ucc.asn.au>
date Thu, 19 Aug 2021 23:17:34 +0800
parents 1051e4eea25a
children
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f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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1 #include "tommath_private.h"
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2 #ifdef BN_MP_MUL_C
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3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
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4 /* SPDX-License-Identifier: Unlicense */
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6 /* high level multiplication (handles sign) */
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7 mp_err mp_mul(const mp_int *a, const mp_int *b, mp_int *c)
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8 {
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9 mp_err err;
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10 int min_len = MP_MIN(a->used, b->used),
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11 max_len = MP_MAX(a->used, b->used),
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12 digs = a->used + b->used + 1;
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13 mp_sign neg = (a->sign == b->sign) ? MP_ZPOS : MP_NEG;
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14
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15 if (MP_HAS(S_MP_BALANCE_MUL) &&
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16 /* Check sizes. The smaller one needs to be larger than the Karatsuba cut-off.
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17 * The bigger one needs to be at least about one MP_KARATSUBA_MUL_CUTOFF bigger
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18 * to make some sense, but it depends on architecture, OS, position of the
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19 * stars... so YMMV.
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20 * Using it to cut the input into slices small enough for fast_s_mp_mul_digs
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21 * was actually slower on the author's machine, but YMMV.
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22 */
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23 (min_len >= MP_KARATSUBA_MUL_CUTOFF) &&
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24 ((max_len / 2) >= MP_KARATSUBA_MUL_CUTOFF) &&
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25 /* Not much effect was observed below a ratio of 1:2, but again: YMMV. */
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26 (max_len >= (2 * min_len))) {
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27 err = s_mp_balance_mul(a,b,c);
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28 } else if (MP_HAS(S_MP_TOOM_MUL) &&
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29 (min_len >= MP_TOOM_MUL_CUTOFF)) {
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30 err = s_mp_toom_mul(a, b, c);
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31 } else if (MP_HAS(S_MP_KARATSUBA_MUL) &&
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32 (min_len >= MP_KARATSUBA_MUL_CUTOFF)) {
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33 err = s_mp_karatsuba_mul(a, b, c);
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34 } else if (MP_HAS(S_MP_MUL_DIGS_FAST) &&
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35 /* can we use the fast multiplier?
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36 *
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37 * The fast multiplier can be used if the output will
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38 * have less than MP_WARRAY digits and the number of
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39 * digits won't affect carry propagation
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40 */
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41 (digs < MP_WARRAY) &&
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42 (min_len <= MP_MAXFAST)) {
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43 err = s_mp_mul_digs_fast(a, b, c, digs);
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44 } else if (MP_HAS(S_MP_MUL_DIGS)) {
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45 err = s_mp_mul_digs(a, b, c, digs);
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46 } else {
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47 err = MP_VAL;
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48 }
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49 c->sign = (c->used > 0) ? neg : MP_ZPOS;
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50 return err;
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51 }
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52 #endif