### view libtommath/bn_mp_cnt_lsb.c @ 1514:6c16a05023aa

rename some options and move some to sysoptions.h
author Matt Johnston Sun, 18 Feb 2018 00:29:17 +0800 8bba51a55704 f52919ffd3b1
line wrap: on
line source
```#include <tommath_private.h>
#ifdef BN_MP_CNT_LSB_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis
*
* LibTomMath is a library that provides multiple-precision
* integer arithmetic as well as number theoretic functionality.
*
* The library was designed directly after the MPI library by
* Michael Fromberger but has been written from scratch with
*
* The library is free for all purposes without any express
* guarantee it works.
*
* Tom St Denis, [email protected], http://libtom.org
*/

static const int lnz = {
4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0
};

/* Counts the number of lsbs which are zero before the first zero bit */
int mp_cnt_lsb(mp_int *a)
{
int x;
mp_digit q, qq;

/* easy out */
if (mp_iszero(a) == MP_YES) {
return 0;
}

/* scan lower digits until non-zero */
for (x = 0; (x < a->used) && (a->dp[x] == 0); x++) {}
q = a->dp[x];
x *= DIGIT_BIT;

/* now scan this digit until a 1 is found */
if ((q & 1) == 0) {
do {
qq  = q & 15;
x  += lnz[qq];
q >>= 4;
} while (qq == 0);
}
return x;
}

#endif

/* ref:         \$Format:%D\$ */
/* git commit:  \$Format:%H\$ */
/* commit time: \$Format:%ai\$ */
```