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annotate tomsfastmath/src/bit/fp_cnt_lsb.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 static const int lnz[16] = {
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13 4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0
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14 };
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16 /* Counts the number of lsbs which are zero before the first zero bit */
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17 int fp_cnt_lsb(fp_int *a)
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18 {
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19 int x;
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20 fp_digit q, qq;
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22 /* easy out */
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23 if (fp_iszero(a) == 1) {
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24 return 0;
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25 }
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27 /* scan lower digits until non-zero */
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28 for (x = 0; x < a->used && a->dp[x] == 0; x++);
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29 q = a->dp[x];
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30 x *= DIGIT_BIT;
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32 /* now scan this digit until a 1 is found */
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33 if ((q & 1) == 0) {
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34 do {
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35 qq = q & 15;
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36 x += lnz[qq];
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37 q >>= 4;
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38 } while (qq == 0);
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39 }
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40 return x;
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41 }
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44 /* $Source$ */
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45 /* $Revision$ */
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46 /* $Date$ */