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38 lines
791 B
38 lines
791 B
#include "tommath_private.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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/* SPDX-License-Identifier: Unlicense */
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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(const 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_IS_ZERO(a)) {
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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] == 0u); x++) {}
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q = a->dp[x];
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x *= MP_DIGIT_BIT;
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/* now scan this digit until a 1 is found */
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if ((q & 1u) == 0u) {
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do {
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qq = q & 15u;
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x += lnz[qq];
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q >>= 4;
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} while (qq == 0u);
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}
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return x;
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}
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#endif
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