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      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 (at) 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 $ */
     86