Mercurial > dropbear

annotate libtommath/bn_mp_reduce_is_2k.c @ 284:eed26cff980b

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propagate from branch 'au.asn.ucc.matt.ltm.dropbear' (head 6c790cad5a7fa866ad062cb3a0c279f7ba788583) to branch 'au.asn.ucc.matt.dropbear' (head fff0894a0399405a9410ea1c6d118f342cf2aa64)
author Matt Johnston <matt@ucc.asn.au>
date Wed, 08 Mar 2006 13:23:49 +0000
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children 5ff8218bcee9
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284
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1 #include <tommath.h>
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2 #ifdef BN_MP_REDUCE_IS_2K_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.org
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16 */
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17
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18 /* determines if mp_reduce_2k can be used */
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19 int mp_reduce_is_2k(mp_int *a)
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20 {
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21 int ix, iy, iw;
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22 mp_digit iz;
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23
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24 if (a->used == 0) {
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25 return MP_NO;
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26 } else if (a->used == 1) {
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27 return MP_YES;
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28 } else if (a->used > 1) {
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29 iy = mp_count_bits(a);
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30 iz = 1;
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31 iw = 1;
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32
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33 /* Test every bit from the second digit up, must be 1 */
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34 for (ix = DIGIT_BIT; ix < iy; ix++) {
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35 if ((a->dp[iw] & iz) == 0) {
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36 return MP_NO;
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37 }
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38 iz <<= 1;
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39 if (iz > (mp_digit)MP_MASK) {
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40 ++iw;
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41 iz = 1;
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42 }
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43 }
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44 }
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45 return MP_YES;
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46 }
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47
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48 #endif