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

   1 #include <tommath.h>
   2 #ifdef BN_MP_MUL_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://math.libtomcrypt.com
  16  */
  17
  18 /* multiply by a digit */
  19 int
  20 mp_mul_d (mp_int * a, mp_digit b, mp_int * c)
  21 {
  22   mp_digit u, *tmpa, *tmpc;
  23   mp_word  r;
  24   int      ix, res, olduse;
  25
  26   /* make sure c is big enough to hold a*b */
  27   if (c->alloc < a->used + 1) {
  28     if ((res = mp_grow (c, a->used + 1)) != MP_OKAY) {
  29       return res;
  30     }
  31   }
  32
  33   /* get the original destinations used count */
  34   olduse = c->used;
  35
  36   /* set the sign */
  37   c->sign = a->sign;
  38
  39   /* alias for a->dp [source] */
  40   tmpa = a->dp;
  41
  42   /* alias for c->dp [dest] */
  43   tmpc = c->dp;
  44
  45   /* zero carry */
  46   u = 0;
  47
  48   /* compute columns */
  49   for (ix = 0; ix < a->used; ix++) {
  50     /* compute product and carry sum for this term */
  51     r       = ((mp_word) u) + ((mp_word)*tmpa++) * ((mp_word)b);
  52
  53     /* mask off higher bits to get a single digit */
  54     *tmpc++ = (mp_digit) (r & ((mp_word) MP_MASK));
  55
  56     /* send carry into next iteration */
  57     u       = (mp_digit) (r >> ((mp_word) DIGIT_BIT));
  58   }
  59
  60   /* store final carry [if any] and increment ix offset  */
  61   *tmpc++ = u;
  62   ++ix;
  63
  64   /* now zero digits above the top */
  65   while (ix++ < olduse) {
  66      *tmpc++ = 0;
  67   }
  68
  69   /* set used count */
  70   c->used = a->used + 1;
  71   mp_clamp(c);
  72
  73   return MP_OKAY;
  74 }
  75 #endif
  76
  77 /* $Source: /cvs/libtom/libtommath/bn_mp_mul_d.c,v $ */
  78 /* $Revision: 1.3 $ */
  79 /* $Date: 2006/03/31 14:18:44 $ */