Line data    Source code

       1             : #include <tommath.h>
       2             : #ifdef BN_MP_EXPT_D_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             : /* calculate c = a**b  using a square-multiply algorithm */
      19           0 : int mp_expt_d (mp_int * a, mp_digit b, mp_int * c)
      20             : {
      21             :   int     res, x;
      22             :   mp_int  g;
      23             : 
      24           0 :   if ((res = mp_init_copy (&g, a)) != MP_OKAY) {
      25           0 :     return res;
      26             :   }
      27             : 
      28             :   /* set initial result */
      29           0 :   mp_set (c, 1);
      30             : 
      31           0 :   for (x = 0; x < (int) DIGIT_BIT; x++) {
      32             :     /* square */
      33           0 :     if ((res = mp_sqr (c, c)) != MP_OKAY) {
      34           0 :       mp_clear (&g);
      35           0 :       return res;
      36             :     }
      37             : 
      38             :     /* if the bit is set multiply */
      39           0 :     if ((b & (mp_digit) (((mp_digit)1) << (DIGIT_BIT - 1))) != 0) {
      40           0 :       if ((res = mp_mul (c, &g, c)) != MP_OKAY) {
      41           0 :          mp_clear (&g);
      42           0 :          return res;
      43             :       }
      44             :     }
      45             : 
      46             :     /* shift to next bit */
      47           0 :     b <<= 1;
      48             :   }
      49             : 
      50           0 :   mp_clear (&g);
      51           0 :   return MP_OKAY;
      52             : }
      53             : #endif
      54             : 
      55             : /* $Source: /cvs/libtom/libtommath/bn_mp_expt_d.c,v $ */
      56             : /* $Revision: 1.4 $ */
      57             : /* $Date: 2006/12/28 01:25:13 $ */