Mercurial > dropbear

annotate libtommath/bn_mp_expt_d.c @ 691:e698d1a9f428

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Some changes since 2012.55
author Matt Johnston <matt@ucc.asn.au>
date Fri, 22 Feb 2013 23:54:47 +0800
parents 5ff8218bcee9
children 60fc6476e044
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1 #include <tommath.h>
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2 #ifdef BN_MP_EXPT_D_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 * The library is free for all purposes without any express
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13 * guarantee it works.
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14 *
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15 * Tom St Denis, [email protected], http://math.libtomcrypt.com
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16 */
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17
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18 /* calculate c = a**b using a square-multiply algorithm */
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19 int mp_expt_d (mp_int * a, mp_digit b, mp_int * c)
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20 {
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21 int res, x;
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22 mp_int g;
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23
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24 if ((res = mp_init_copy (&g, a)) != MP_OKAY) {
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25 return res;
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26 }
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27
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28 /* set initial result */
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29 mp_set (c, 1);
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30
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31 for (x = 0; x < (int) DIGIT_BIT; x++) {
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32 /* square */
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33 if ((res = mp_sqr (c, c)) != MP_OKAY) {
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34 mp_clear (&g);
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35 return res;
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36 }
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38 /* if the bit is set multiply */
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39 if ((b & (mp_digit) (((mp_digit)1) << (DIGIT_BIT - 1))) != 0) {
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40 if ((res = mp_mul (c, &g, c)) != MP_OKAY) {
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41 mp_clear (&g);
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42 return res;
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43 }
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44 }
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45
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46 /* shift to next bit */
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47 b <<= 1;
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48 }
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49
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50 mp_clear (&g);
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51 return MP_OKAY;
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52 }
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53 #endif
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54
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55 /* $Source: /cvs/libtom/libtommath/bn_mp_expt_d.c,v $ */
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56 /* $Revision: 1.3 $ */
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57 /* $Date: 2006/03/31 14:18:44 $ */