### view libtommath/bn_mp_cnt_lsb.c @ 457:e430a26064eeDROPBEAR_0.50

Make dropbearkey only generate 1024 bit keys
author Matt Johnston Wed, 08 Aug 2007 15:57:50 +0000 5ff8218bcee9 60fc6476e044
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```#include <tommath.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
* additional optimizations in place.
*
* The library is free for all purposes without any express
* guarantee it works.
*
* Tom St Denis, [email protected], http://math.libtomcrypt.com
*/

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) == 1) {
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

/* \$Source: /cvs/libtom/libtommath/bn_mp_cnt_lsb.c,v \$ */
/* \$Revision: 1.3 \$ */
/* \$Date: 2006/03/31 14:18:44 \$ */
```