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annotate tomsfastmath/src/bit/fp_div_2.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 /* b = a/2 */
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13 void fp_div_2(fp_int * a, fp_int * b)
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14 {
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15 int x, oldused;
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17 oldused = b->used;
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18 b->used = a->used;
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19 {
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20 register fp_digit r, rr, *tmpa, *tmpb;
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22 /* source alias */
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23 tmpa = a->dp + b->used - 1;
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25 /* dest alias */
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26 tmpb = b->dp + b->used - 1;
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28 /* carry */
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29 r = 0;
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30 for (x = b->used - 1; x >= 0; x--) {
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31 /* get the carry for the next iteration */
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32 rr = *tmpa & 1;
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34 /* shift the current digit, add in carry and store */
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35 *tmpb-- = (*tmpa-- >> 1) | (r << (DIGIT_BIT - 1));
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37 /* forward carry to next iteration */
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38 r = rr;
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39 }
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41 /* zero excess digits */
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42 tmpb = b->dp + b->used;
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43 for (x = b->used; x < oldused; x++) {
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44 *tmpb++ = 0;
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45 }
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46 }
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47 b->sign = a->sign;
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48 fp_clamp (b);
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49 }
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51 /* $Source$ */
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52 /* $Revision$ */
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53 /* $Date$ */