/home/ntakagi/work/tcl8.5.1/libtommath/bn_mp_count_bits.c Source File

00001 #include <tommath.h>
00002 #ifdef BN_MP_COUNT_BITS_C
00003 /* LibTomMath, multiple-precision integer library -- Tom St Denis
00004  *
00005  * LibTomMath is a library that provides multiple-precision
00006  * integer arithmetic as well as number theoretic functionality.
00007  *
00008  * The library was designed directly after the MPI library by
00009  * Michael Fromberger but has been written from scratch with
00010  * additional optimizations in place.
00011  *
00012  * The library is free for all purposes without any express
00013  * guarantee it works.
00014  *
00015  * Tom St Denis, tomstdenis@gmail.com, http://math.libtomcrypt.com
00016  */
00017 
00018 /* returns the number of bits in an int */
00019 int
00020 mp_count_bits (mp_int * a)
00021 {
00022   int     r;
00023   mp_digit q;
00024 
00025   /* shortcut */
00026   if (a->used == 0) {
00027     return 0;
00028   }
00029 
00030   /* get number of digits and add that */
00031   r = (a->used - 1) * DIGIT_BIT;
00032   
00033   /* take the last digit and count the bits in it */
00034   q = a->dp[a->used - 1];
00035   while (q > ((mp_digit) 0)) {
00036     ++r;
00037     q >>= ((mp_digit) 1);
00038   }
00039   return r;
00040 }
00041 #endif
00042 
00043 /* $Source: /cvsroot/tcl/libtommath/bn_mp_count_bits.c,v $ */
00044 /* $Revision: 1.1.1.3 $ */
00045 /* $Date: 2006/12/01 00:08:11 $ */