release/src/router/dropbear/libtommath/bn_mp_2expt.c

   1 #include <tommath.h>
   2 #ifdef BN_MP_2EXPT_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 /* computes a = 2**b
  19  *
  20  * Simple algorithm which zeroes the int, grows it then just sets one bit
  21  * as required.
  22  */
  23 int
  24 mp_2expt (mp_int * a, int b)
  25 {
  26   int     res;
  27
  28   /* zero a as per default */
  29   mp_zero (a);
  30
  31   /* grow a to accomodate the single bit */
  32   if ((res = mp_grow (a, b / DIGIT_BIT + 1)) != MP_OKAY) {
  33     return res;
  34   }
  35
  36   /* set the used count of where the bit will go */
  37   a->used = b / DIGIT_BIT + 1;
  38
  39   /* put the single bit in its place */
  40   a->dp[b / DIGIT_BIT] = ((mp_digit)1) << (b % DIGIT_BIT);
  41
  42   return MP_OKAY;
  43 }
  44 #endif
  45
  46 /* $Source: /cvs/libtom/libtommath/bn_mp_2expt.c,v $ */
  47 /* $Revision: 1.3 $ */
  48 /* $Date: 2006/03/31 14:18:44 $ */