Line data    Source code

       1             : #include <tommath.h>
       2             : #ifdef BN_MP_MOD_2D_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://libtom.org
      16             :  */
      17             : 
      18             : /* calc a value mod 2**b */
      19             : int
      20           0 : mp_mod_2d (mp_int * a, int b, mp_int * c)
      21             : {
      22             :   int     x, res;
      23             : 
      24             :   /* if b is <= 0 then zero the int */
      25           0 :   if (b <= 0) {
      26           0 :     mp_zero (c);
      27           0 :     return MP_OKAY;
      28             :   }
      29             : 
      30             :   /* if the modulus is larger than the value than return */
      31           0 :   if (b >= (int) (a->used * DIGIT_BIT)) {
      32           0 :     res = mp_copy (a, c);
      33           0 :     return res;
      34             :   }
      35             : 
      36             :   /* copy */
      37           0 :   if ((res = mp_copy (a, c)) != MP_OKAY) {
      38           0 :     return res;
      39             :   }
      40             : 
      41             :   /* zero digits above the last digit of the modulus */
      42           0 :   for (x = (b / DIGIT_BIT) + ((b % DIGIT_BIT) == 0 ? 0 : 1); x < c->used; x++) {
      43           0 :     c->dp[x] = 0;
      44             :   }
      45             :   /* clear the digit that is not completely outside/inside the modulus */
      46           0 :   c->dp[b / DIGIT_BIT] &=
      47           0 :     (mp_digit) ((((mp_digit) 1) << (((mp_digit) b) % DIGIT_BIT)) - ((mp_digit) 1));
      48           0 :   mp_clamp (c);
      49           0 :   return MP_OKAY;
      50             : }
      51             : #endif
      52             : 
      53             : /* $Source: /cvs/libtom/libtommath/bn_mp_mod_2d.c,v $ */
      54             : /* $Revision: 1.4 $ */
      55             : /* $Date: 2006/12/28 01:25:13 $ */