Mercurial > dropbear

annotate libtommath/bn_s_mp_mul_high_digs.c @ 1667:986126448688

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Update remaining advise to edit options.h You should edit localoptions.h instead.
author Alexander Dahl <ada@thorsis.com>
date Tue, 10 Mar 2020 15:38:38 +0100
parents f52919ffd3b1
children 1051e4eea25a
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1 #include "tommath_private.h"
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2 #ifdef BN_S_MP_MUL_HIGH_DIGS_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 /* multiplies |a| * |b| and does not compute the lower digs digits
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16 * [meant to get the higher part of the product]
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17 */
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18 int s_mp_mul_high_digs(const mp_int *a, const mp_int *b, mp_int *c, int digs)
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19 {
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20 mp_int t;
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21 int res, pa, pb, ix, iy;
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22 mp_digit u;
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23 mp_word r;
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24 mp_digit tmpx, *tmpt, *tmpy;
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26 /* can we use the fast multiplier? */
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27 #ifdef BN_FAST_S_MP_MUL_HIGH_DIGS_C
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28 if (((a->used + b->used + 1) < (int)MP_WARRAY)
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29 && (MIN(a->used, b->used) < (int)(1u << (((size_t)CHAR_BIT * sizeof(mp_word)) - (2u * (size_t)DIGIT_BIT))))) {
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30 return fast_s_mp_mul_high_digs(a, b, c, digs);
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31 }
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32 #endif
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33
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34 if ((res = mp_init_size(&t, a->used + b->used + 1)) != MP_OKAY) {
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35 return res;
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36 }
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37 t.used = a->used + b->used + 1;
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38
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39 pa = a->used;
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40 pb = b->used;
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41 for (ix = 0; ix < pa; ix++) {
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42 /* clear the carry */
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43 u = 0;
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44
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45 /* left hand side of A[ix] * B[iy] */
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46 tmpx = a->dp[ix];
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47
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48 /* alias to the address of where the digits will be stored */
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49 tmpt = &(t.dp[digs]);
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51 /* alias for where to read the right hand side from */
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52 tmpy = b->dp + (digs - ix);
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53
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54 for (iy = digs - ix; iy < pb; iy++) {
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55 /* calculate the double precision result */
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56 r = (mp_word)*tmpt +
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57 ((mp_word)tmpx * (mp_word)*tmpy++) +
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58 (mp_word)u;
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59
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60 /* get the lower part */
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61 *tmpt++ = (mp_digit)(r & (mp_word)MP_MASK);
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62
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63 /* carry the carry */
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64 u = (mp_digit)(r >> (mp_word)DIGIT_BIT);
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65 }
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66 *tmpt = u;
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67 }
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68 mp_clamp(&t);
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69 mp_exch(&t, c);
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70 mp_clear(&t);
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71 return MP_OKAY;
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72 }
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73 #endif
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75 /* ref: HEAD -> master, tag: v1.1.0 */
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76 /* git commit: 08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */
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77 /* commit time: 2019-01-28 20:32:32 +0100 */