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annotate libtommath/bn_mp_mul.c @ 1663:c795520269f9

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Fallback for key gen without hard link support (#89) Add a non-atomic fallback for key generation on platforms where link() is not permitted (such as most stock Android installs) or on filesystems without hard link support (such as FAT).
author Matt Robinson <git@nerdoftheherd.com>
date Sat, 14 Mar 2020 14:37:35 +0000
parents f52919ffd3b1
children 1051e4eea25a
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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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 *
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5 * LibTomMath is a library that provides multiple-precision
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6 * integer arithmetic as well as number theoretic functionality.
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7 *
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8 * The library was designed directly after the MPI library by
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9 * Michael Fromberger but has been written from scratch with
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10 * additional optimizations in place.
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11 *
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12 * SPDX-License-Identifier: Unlicense
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13 */
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14
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15 /* high level multiplication (handles sign) */
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16 int mp_mul(const mp_int *a, const mp_int *b, mp_int *c)
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17 {
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18 int res, neg;
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19 neg = (a->sign == b->sign) ? MP_ZPOS : MP_NEG;
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20
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21 /* use Toom-Cook? */
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22 #ifdef BN_MP_TOOM_MUL_C
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23 if (MIN(a->used, b->used) >= TOOM_MUL_CUTOFF) {
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24 res = mp_toom_mul(a, b, c);
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25 } else
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26 #endif
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27 #ifdef BN_MP_KARATSUBA_MUL_C
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28 /* use Karatsuba? */
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29 if (MIN(a->used, b->used) >= KARATSUBA_MUL_CUTOFF) {
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30 res = mp_karatsuba_mul(a, b, c);
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31 } else
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32 #endif
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33 {
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34 /* can we use the fast multiplier?
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35 *
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36 * The fast multiplier can be used if the output will
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37 * have less than MP_WARRAY digits and the number of
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38 * digits won't affect carry propagation
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39 */
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40 int digs = a->used + b->used + 1;
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41
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42 #ifdef BN_FAST_S_MP_MUL_DIGS_C
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43 if ((digs < (int)MP_WARRAY) &&
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44 (MIN(a->used, b->used) <=
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45 (int)(1u << (((size_t)CHAR_BIT * sizeof(mp_word)) - (2u * (size_t)DIGIT_BIT))))) {
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46 res = fast_s_mp_mul_digs(a, b, c, digs);
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47 } else
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48 #endif
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49 {
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50 #ifdef BN_S_MP_MUL_DIGS_C
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51 res = s_mp_mul(a, b, c); /* uses s_mp_mul_digs */
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52 #else
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53 res = MP_VAL;
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54 #endif
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55 }
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56 }
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57 c->sign = (c->used > 0) ? neg : MP_ZPOS;
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58 return res;
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59 }
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60 #endif
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61
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62 /* ref: HEAD -> master, tag: v1.1.0 */
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63 /* git commit: 08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */
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64 /* commit time: 2019-01-28 20:32:32 +0100 */