release/src/router/dropbear/libtommath/bn_mp_reduce_is_2k.c

   1 #include <tommath.h>
   2 #ifdef BN_MP_REDUCE_IS_2K_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 /* determines if mp_reduce_2k can be used */
  19 int mp_reduce_is_2k(mp_int *a)
  20 {
  21    int ix, iy, iw;
  22    mp_digit iz;
  23
  24    if (a->used == 0) {
  25       return MP_NO;
  26    } else if (a->used == 1) {
  27       return MP_YES;
  28    } else if (a->used > 1) {
  29       iy = mp_count_bits(a);
  30       iz = 1;
  31       iw = 1;
  32
  33       /* Test every bit from the second digit up, must be 1 */
  34       for (ix = DIGIT_BIT; ix < iy; ix++) {
  35           if ((a->dp[iw] & iz) == 0) {
  36              return MP_NO;
  37           }
  38           iz <<= 1;
  39           if (iz > (mp_digit)MP_MASK) {
  40              ++iw;
  41              iz = 1;
  42           }
  43       }
  44    }
  45    return MP_YES;
  46 }
  47
  48 #endif
  49
  50 /* $Source: /cvs/libtom/libtommath/bn_mp_reduce_is_2k.c,v $ */
  51 /* $Revision: 1.3 $ */
  52 /* $Date: 2006/03/31 14:18:44 $ */