54 lines
1.2 KiB
C
54 lines
1.2 KiB
C
#include <tommath.h>
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#ifdef BN_MP_CNT_LSB_C
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/* LibTomMath, multiple-precision integer library -- Tom St Denis
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*
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* LibTomMath is a library that provides multiple-precision
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* integer arithmetic as well as number theoretic functionality.
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*
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* The library was designed directly after the MPI library by
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* Michael Fromberger but has been written from scratch with
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* additional optimizations in place.
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*
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* The library is free for all purposes without any express
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* guarantee it works.
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*
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* Tom St Denis, tomstdenis@iahu.ca, http://math.libtomcrypt.org
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*/
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static const int lnz[16] = {
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4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0
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};
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/* Counts the number of lsbs which are zero before the first zero bit */
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int mp_cnt_lsb(mp_int *a)
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{
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int x;
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mp_digit q, qq;
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/* easy out */
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if (mp_iszero(a) == 1) {
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return 0;
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}
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/* scan lower digits until non-zero */
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for (x = 0; x < a->used && a->dp[x] == 0; x++);
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q = a->dp[x];
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x *= DIGIT_BIT;
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/* now scan this digit until a 1 is found */
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if ((q & 1) == 0) {
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do {
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qq = q & 15;
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x += lnz[qq];
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q >>= 4;
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} while (qq == 0);
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}
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return x;
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}
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#endif
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/* $Source$ */
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/* $Revision$ */
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/* $Date$ */
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