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 #include #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, tomstdenis@gmail.com, http://math.libtomcrypt.com */ static const int lnz[16] = { 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 \$ */