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annotate libtommath/bn_mp_2expt.c @ 1611:0196f4f83fee

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author Matt Johnston <matt@ucc.asn.au>
date Tue, 24 Jul 2018 20:19:05 +0800
parents 8bba51a55704
children f52919ffd3b1
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1 #include <tommath_private.h>
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2 #ifdef BN_MP_2EXPT_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://libtom.org
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16 */
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17
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18 /* computes a = 2**b
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19 *
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20 * Simple algorithm which zeroes the int, grows it then just sets one bit
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21 * as required.
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22 */
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23 int
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24 mp_2expt (mp_int * a, int b)
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25 {
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26 int res;
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28 /* zero a as per default */
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29 mp_zero (a);
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31 /* grow a to accomodate the single bit */
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32 if ((res = mp_grow (a, (b / DIGIT_BIT) + 1)) != MP_OKAY) {
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33 return res;
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34 }
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36 /* set the used count of where the bit will go */
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37 a->used = (b / DIGIT_BIT) + 1;
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39 /* put the single bit in its place */
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40 a->dp[b / DIGIT_BIT] = ((mp_digit)1) << (b % DIGIT_BIT);
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42 return MP_OKAY;
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43 }
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44 #endif
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45
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46 /* ref: $Format:%D$ */
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47 /* git commit: $Format:%H$ */
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48 /* commit time: $Format:%ai$ */