release/src/router/dropbear/libtommath/bn_mp_mul_2.c

   1 #include <tommath.h>
   2 #ifdef BN_MP_MUL_2_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 /* b = a*2 */
  19 int mp_mul_2(mp_int * a, mp_int * b)
  20 {
  21   int     x, res, oldused;
  22
  23   /* grow to accomodate result */
  24   if (b->alloc < a->used + 1) {
  25     if ((res = mp_grow (b, a->used + 1)) != MP_OKAY) {
  26       return res;
  27     }
  28   }
  29
  30   oldused = b->used;
  31   b->used = a->used;
  32
  33   {
  34     register mp_digit r, rr, *tmpa, *tmpb;
  35
  36     /* alias for source */
  37     tmpa = a->dp;
  38
  39     /* alias for dest */
  40     tmpb = b->dp;
  41
  42     /* carry */
  43     r = 0;
  44     for (x = 0; x < a->used; x++) {
  45
  46       /* get what will be the *next* carry bit from the
  47        * MSB of the current digit
  48        */
  49       rr = *tmpa >> ((mp_digit)(DIGIT_BIT - 1));
  50
  51       /* now shift up this digit, add in the carry [from the previous] */
  52       *tmpb++ = ((*tmpa++ << ((mp_digit)1)) | r) & MP_MASK;
  53
  54       /* copy the carry that would be from the source
  55        * digit into the next iteration
  56        */
  57       r = rr;
  58     }
  59
  60     /* new leading digit? */
  61     if (r != 0) {
  62       /* add a MSB which is always 1 at this point */
  63       *tmpb = 1;
  64       ++(b->used);
  65     }
  66
  67     /* now zero any excess digits on the destination
  68      * that we didn't write to
  69      */
  70     tmpb = b->dp + b->used;
  71     for (x = b->used; x < oldused; x++) {
  72       *tmpb++ = 0;
  73     }
  74   }
  75   b->sign = a->sign;
  76   return MP_OKAY;
  77 }
  78 #endif
  79
  80 /* $Source: /cvs/libtom/libtommath/bn_mp_mul_2.c,v $ */
  81 /* $Revision: 1.3 $ */
  82 /* $Date: 2006/03/31 14:18:44 $ */