From 1c5fda515f96c27d4e3b732d887f418453f1cb14 Mon Sep 17 00:00:00 2001 From: Matt Johnston Date: Wed, 8 Mar 2006 13:16:18 +0000 Subject: Import of libtommath 0.35 From ltm-0.35.tar.bz2 SHA1 of 3f193dbae9351e92d02530994fa18236f7fde01c --HG-- branch : libtommath-orig extra : convert_revision : 2b4b13ac88b2a81e5c86ba868c92c6a452630e02 --- bn_mp_cnt_lsb.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 49 insertions(+) create mode 100644 bn_mp_cnt_lsb.c (limited to 'bn_mp_cnt_lsb.c') diff --git a/bn_mp_cnt_lsb.c b/bn_mp_cnt_lsb.c new file mode 100644 index 0000000..571f03f --- /dev/null +++ b/bn_mp_cnt_lsb.c @@ -0,0 +1,49 @@ +#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@iahu.ca, http://math.libtomcrypt.org + */ + +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 -- cgit v1.2.3