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annotate bn_mp_reduce_2k_setup.c @ 2:86e0b50a9b58 libtommath-orig ltm-0.30-orig

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ltm 0.30 orig import
author Matt Johnston <matt@ucc.asn.au>
date Mon, 31 May 2004 18:25:22 +0000
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children d29b64170cf0
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1 /* LibTomMath, multiple-precision integer library -- Tom St Denis
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2 *
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3 * LibTomMath is a library that provides multiple-precision
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4 * integer arithmetic as well as number theoretic functionality.
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5 *
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6 * The library was designed directly after the MPI library by
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7 * Michael Fromberger but has been written from scratch with
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8 * additional optimizations in place.
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9 *
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10 * The library is free for all purposes without any express
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11 * guarantee it works.
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12 *
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13 * Tom St Denis, [email protected], http://math.libtomcrypt.org
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14 */
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15 #include <tommath.h>
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16
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17 /* determines the setup value */
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18 int
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19 mp_reduce_2k_setup(mp_int *a, mp_digit *d)
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20 {
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21 int res, p;
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22 mp_int tmp;
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23
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24 if ((res = mp_init(&tmp)) != MP_OKAY) {
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25 return res;
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26 }
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27
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28 p = mp_count_bits(a);
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29 if ((res = mp_2expt(&tmp, p)) != MP_OKAY) {
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30 mp_clear(&tmp);
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31 return res;
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32 }
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33
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34 if ((res = s_mp_sub(&tmp, a, &tmp)) != MP_OKAY) {
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35 mp_clear(&tmp);
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36 return res;
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37 }
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38
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39 *d = tmp.dp[0];
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40 mp_clear(&tmp);
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41 return MP_OKAY;
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42 }