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annotate libtommath/bn_s_mp_balance_mul.c @ 1868:66a3fabe4870

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merge
author Matt Johnston <matt@ucc.asn.au>
date Tue, 01 Feb 2022 15:51:01 +0800
parents 1051e4eea25a
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
1692
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
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1 #include "tommath_private.h"
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
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2 #ifdef BN_S_MP_BALANCE_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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5
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6 /* single-digit multiplication with the smaller number as the single-digit */
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7 mp_err s_mp_balance_mul(const mp_int *a, const mp_int *b, mp_int *c)
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8 {
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9 int count, len_a, len_b, nblocks, i, j, bsize;
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10 mp_int a0, tmp, A, B, r;
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11 mp_err err;
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12
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13 len_a = a->used;
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14 len_b = b->used;
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15
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16 nblocks = MP_MAX(a->used, b->used) / MP_MIN(a->used, b->used);
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17 bsize = MP_MIN(a->used, b->used) ;
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18
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19 if ((err = mp_init_size(&a0, bsize + 2)) != MP_OKAY) {
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20 return err;
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21 }
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22 if ((err = mp_init_multi(&tmp, &r, NULL)) != MP_OKAY) {
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23 mp_clear(&a0);
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24 return err;
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25 }
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26
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27 /* Make sure that A is the larger one*/
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28 if (len_a < len_b) {
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29 B = *a;
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30 A = *b;
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31 } else {
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32 A = *a;
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33 B = *b;
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34 }
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35
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36 for (i = 0, j=0; i < nblocks; i++) {
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37 /* Cut a slice off of a */
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38 a0.used = 0;
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39 for (count = 0; count < bsize; count++) {
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40 a0.dp[count] = A.dp[ j++ ];
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41 a0.used++;
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42 }
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43 mp_clamp(&a0);
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44 /* Multiply with b */
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45 if ((err = mp_mul(&a0, &B, &tmp)) != MP_OKAY) {
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46 goto LBL_ERR;
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47 }
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48 /* Shift tmp to the correct position */
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49 if ((err = mp_lshd(&tmp, bsize * i)) != MP_OKAY) {
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50 goto LBL_ERR;
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51 }
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52 /* Add to output. No carry needed */
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53 if ((err = mp_add(&r, &tmp, &r)) != MP_OKAY) {
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54 goto LBL_ERR;
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55 }
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56 }
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57 /* The left-overs; there are always left-overs */
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58 if (j < A.used) {
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59 a0.used = 0;
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60 for (count = 0; j < A.used; count++) {
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61 a0.dp[count] = A.dp[ j++ ];
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62 a0.used++;
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63 }
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64 mp_clamp(&a0);
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65 if ((err = mp_mul(&a0, &B, &tmp)) != MP_OKAY) {
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66 goto LBL_ERR;
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67 }
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68 if ((err = mp_lshd(&tmp, bsize * i)) != MP_OKAY) {
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69 goto LBL_ERR;
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70 }
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71 if ((err = mp_add(&r, &tmp, &r)) != MP_OKAY) {
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72 goto LBL_ERR;
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73 }
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74 }
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75
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76 mp_exch(&r,c);
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77 LBL_ERR:
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78 mp_clear_multi(&a0, &tmp, &r,NULL);
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79 return err;
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80 }
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81 #endif