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annotate libtommath/bn_mp_expt_u32.c @ 1825:7a0068effc65

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author Matt Johnston <matt@ucc.asn.au>
date Mon, 11 Oct 2021 15:12:22 +0800
parents 1051e4eea25a
children
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1692
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
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1 #include "tommath_private.h"
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2 #ifdef BN_MP_EXPT_U32_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 /* calculate c = a**b using a square-multiply algorithm */
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7 mp_err mp_expt_u32(const mp_int *a, uint32_t b, mp_int *c)
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8 {
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9 mp_err err;
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10
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11 mp_int g;
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12
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13 if ((err = mp_init_copy(&g, a)) != MP_OKAY) {
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14 return err;
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15 }
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16
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17 /* set initial result */
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18 mp_set(c, 1uL);
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19
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20 while (b > 0u) {
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21 /* if the bit is set multiply */
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22 if ((b & 1u) != 0u) {
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23 if ((err = mp_mul(c, &g, c)) != MP_OKAY) {
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24 goto LBL_ERR;
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25 }
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26 }
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27
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28 /* square */
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29 if (b > 1u) {
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30 if ((err = mp_sqr(&g, &g)) != MP_OKAY) {
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31 goto LBL_ERR;
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32 }
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33 }
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34
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35 /* shift to next bit */
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36 b >>= 1;
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37 }
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38
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39 err = MP_OKAY;
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40
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41 LBL_ERR:
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42 mp_clear(&g);
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43 return err;
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44 }
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45
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46 #endif