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annotate tomsfastmath/src/bit/fp_mod_2d.c @ 645:8622ee48fab5 dropbear-tfm

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- Work around broken asm constraint behaviour on 32bit x86 OS X
author Matt Johnston <matt@ucc.asn.au>
date Wed, 30 Nov 2011 22:27:26 +0800
parents a362b62d38b2
children
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1 /* TomsFastMath, a fast ISO C bignum library.
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2 *
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3 * This project is meant to fill in where LibTomMath
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4 * falls short. That is speed ;-)
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5 *
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6 * This project is public domain and free for all purposes.
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7 *
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8 * Tom St Denis, [email protected]
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9 */
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10 #include <tfm.h>
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12 /* c = a mod 2**d */
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13 void fp_mod_2d(fp_int *a, int b, fp_int *c)
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14 {
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15 int x;
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17 /* zero if count less than or equal to zero */
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18 if (b <= 0) {
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19 fp_zero(c);
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20 return;
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21 }
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23 /* get copy of input */
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24 fp_copy(a, c);
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26 /* if 2**d is larger than we just return */
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27 if (b >= (DIGIT_BIT * a->used)) {
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28 return;
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29 }
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31 /* zero digits above the last digit of the modulus */
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32 for (x = (b / DIGIT_BIT) + ((b % DIGIT_BIT) == 0 ? 0 : 1); x < c->used; x++) {
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33 c->dp[x] = 0;
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34 }
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35 /* clear the digit that is not completely outside/inside the modulus */
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36 c->dp[b / DIGIT_BIT] &= ~((fp_digit)0) >> (DIGIT_BIT - b);
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37 fp_clamp (c);
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38 }
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40 /* $Source$ */
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41 /* $Revision$ */
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42 /* $Date$ */