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annotate tomsfastmath/src/addsub/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 /* c = a - b */
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13 void fp_sub(fp_int *a, fp_int *b, fp_int *c)
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14 {
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15 int sa, sb;
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17 sa = a->sign;
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18 sb = b->sign;
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20 if (sa != sb) {
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21 /* subtract a negative from a positive, OR */
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22 /* subtract a positive from a negative. */
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23 /* In either case, ADD their magnitudes, */
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24 /* and use the sign of the first number. */
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25 c->sign = sa;
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26 s_fp_add (a, b, c);
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27 } else {
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28 /* subtract a positive from a positive, OR */
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29 /* subtract a negative from a negative. */
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30 /* First, take the difference between their */
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31 /* magnitudes, then... */
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32 if (fp_cmp_mag (a, b) != FP_LT) {
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33 /* Copy the sign from the first */
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34 c->sign = sa;
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35 /* The first has a larger or equal magnitude */
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36 s_fp_sub (a, b, c);
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37 } else {
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38 /* The result has the *opposite* sign from */
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39 /* the first number. */
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40 c->sign = (sa == FP_ZPOS) ? FP_NEG : FP_ZPOS;
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41 /* The second has a larger magnitude */
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42 s_fp_sub (b, a, c);
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43 }
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44 }
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45 }
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46
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48 /* $Source$ */
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49 /* $Revision$ */
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50 /* $Date$ */