Mercurial > dropbear

annotate libtommath/bn_mp_get_int.c @ 409:0e69e948caba

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Add comments about requiring keysize <= 2*SHA1_HASH_SIZE
author Matt Johnston <matt@ucc.asn.au>
date Sun, 04 Feb 2007 10:31:48 +0000
parents eed26cff980b
children 5ff8218bcee9
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1 #include <tommath.h>
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2 #ifdef BN_MP_GET_INT_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 /* get the lower 32-bits of an mp_int */
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19 unsigned long mp_get_int(mp_int * a)
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20 {
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21 int i;
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22 unsigned long res;
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23
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24 if (a->used == 0) {
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25 return 0;
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26 }
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27
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28 /* get number of digits of the lsb we have to read */
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29 i = MIN(a->used,(int)((sizeof(unsigned long)*CHAR_BIT+DIGIT_BIT-1)/DIGIT_BIT))-1;
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30
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31 /* get most significant digit of result */
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32 res = DIGIT(a,i);
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33
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34 while (--i >= 0) {
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35 res = (res << DIGIT_BIT) | DIGIT(a,i);
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36 }
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37
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38 /* force result to 32-bits always so it is consistent on non 32-bit platforms */
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39 return res & 0xFFFFFFFFUL;
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40 }
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41 #endif