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annotate tomsfastmath/src/addsub/s_fp_sub.c @ 643:a362b62d38b2 dropbear-tfm

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Add tomsfastmath from git rev bfa4582842bc3bab42e4be4aed5703437049502a with Makefile.in renamed
author Matt Johnston <matt@ucc.asn.au>
date Wed, 23 Nov 2011 18:10:20 +0700
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a362b62d38b2 Add tomsfastmath from git rev bfa4582842bc3bab42e4be4aed5703437049502a
Matt Johnston <matt@ucc.asn.au>
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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 /* unsigned subtraction ||a|| >= ||b|| ALWAYS! */
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13 void s_fp_sub(fp_int *a, fp_int *b, fp_int *c)
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14 {
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15 int x, oldbused, oldused;
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16 fp_word t;
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18 oldused = c->used;
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19 oldbused = b->used;
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20 c->used = a->used;
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21 t = 0;
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22 for (x = 0; x < oldbused; x++) {
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23 t = ((fp_word)a->dp[x]) - (((fp_word)b->dp[x]) + t);
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24 c->dp[x] = (fp_digit)t;
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25 t = (t >> DIGIT_BIT)&1;
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26 }
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27 for (; x < a->used; x++) {
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28 t = ((fp_word)a->dp[x]) - t;
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29 c->dp[x] = (fp_digit)t;
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30 t = (t >> DIGIT_BIT)&1;
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31 }
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32 for (; x < oldused; x++) {
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33 c->dp[x] = 0;
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34 }
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35 fp_clamp(c);
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36 }
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38 /* $Source$ */
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39 /* $Revision$ */
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40 /* $Date$ */