release/src/router/dropbear/libtommath/bn_mp_mul_2d.c

   1 #include <tommath.h>
   2 #ifdef BN_MP_MUL_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://math.libtomcrypt.com
  16  */
  17
  18 /* shift left by a certain bit count */
  19 int mp_mul_2d (mp_int * a, int b, mp_int * c)
  20 {
  21   mp_digit d;
  22   int      res;
  23
  24   /* copy */
  25   if (a != c) {
  26      if ((res = mp_copy (a, c)) != MP_OKAY) {
  27        return res;
  28      }
  29   }
  30
  31   if (c->alloc < (int)(c->used + b/DIGIT_BIT + 1)) {
  32      if ((res = mp_grow (c, c->used + b / DIGIT_BIT + 1)) != MP_OKAY) {
  33        return res;
  34      }
  35   }
  36
  37   /* shift by as many digits in the bit count */
  38   if (b >= (int)DIGIT_BIT) {
  39     if ((res = mp_lshd (c, b / DIGIT_BIT)) != MP_OKAY) {
  40       return res;
  41     }
  42   }
  43
  44   /* shift any bit count < DIGIT_BIT */
  45   d = (mp_digit) (b % DIGIT_BIT);
  46   if (d != 0) {
  47     register mp_digit *tmpc, shift, mask, r, rr;
  48     register int x;
  49
  50     /* bitmask for carries */
  51     mask = (((mp_digit)1) << d) - 1;
  52
  53     /* shift for msbs */
  54     shift = DIGIT_BIT - d;
  55
  56     /* alias */
  57     tmpc = c->dp;
  58
  59     /* carry */
  60     r    = 0;
  61     for (x = 0; x < c->used; x++) {
  62       /* get the higher bits of the current word */
  63       rr = (*tmpc >> shift) & mask;
  64
  65       /* shift the current word and OR in the carry */
  66       *tmpc = ((*tmpc << d) | r) & MP_MASK;
  67       ++tmpc;
  68
  69       /* set the carry to the carry bits of the current word */
  70       r = rr;
  71     }
  72
  73     /* set final carry */
  74     if (r != 0) {
  75        c->dp[(c->used)++] = r;
  76     }
  77   }
  78   mp_clamp (c);
  79   return MP_OKAY;
  80 }
  81 #endif
  82
  83 /* $Source: /cvs/libtom/libtommath/bn_mp_mul_2d.c,v $ */
  84 /* $Revision: 1.3 $ */
  85 /* $Date: 2006/03/31 14:18:44 $ */