release/src/router/dropbear/libtommath/bn_mp_count_bits.c

   1 #include <tommath.h>
   2 #ifdef BN_MP_COUNT_BITS_C
   3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
   4  *
   5  * LibTomMath is a library that provides multiple-precision
   6  * integer arithmetic as well as number theoretic functionality.
   7  *
   8  * The library was designed directly after the MPI library by
   9  * Michael Fromberger but has been written from scratch with
  10  * additional optimizations in place.
  11  *
  12  * The library is free for all purposes without any express
  13  * guarantee it works.
  14  *
  15  * Tom St Denis, tomstdenis@gmail.com, http://math.libtomcrypt.com
  16  */
  17
  18 /* returns the number of bits in an int */
  19 int
  20 mp_count_bits (mp_int * a)
  21 {
  22   int     r;
  23   mp_digit q;
  24
  25   /* shortcut */
  26   if (a->used == 0) {
  27     return 0;
  28   }
  29
  30   /* get number of digits and add that */
  31   r = (a->used - 1) * DIGIT_BIT;
  32
  33   /* take the last digit and count the bits in it */
  34   q = a->dp[a->used - 1];
  35   while (q > ((mp_digit) 0)) {
  36     ++r;
  37     q >>= ((mp_digit) 1);
  38   }
  39   return r;
  40 }
  41 #endif
  42
  43 /* $Source: /cvs/libtom/libtommath/bn_mp_count_bits.c,v $ */
  44 /* $Revision: 1.3 $ */
  45 /* $Date: 2006/03/31 14:18:44 $ */