Line data    Source code

       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://libtom.org
      16             :  */
      17             : 
      18             : /* multiply by a digit */
      19             : int
      20      188355 : 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      188355 :   if (c->alloc < a->used + 1) {
      28        1154 :     if ((res = mp_grow (c, a->used + 1)) != MP_OKAY) {
      29           0 :       return res;
      30             :     }
      31             :   }
      32             : 
      33             :   /* get the original destinations used count */
      34      188355 :   olduse = c->used;
      35             : 
      36             :   /* set the sign */
      37      188355 :   c->sign = a->sign;
      38             : 
      39             :   /* alias for a->dp [source] */
      40      188355 :   tmpa = a->dp;
      41             : 
      42             :   /* alias for c->dp [dest] */
      43      188355 :   tmpc = c->dp;
      44             : 
      45             :   /* zero carry */
      46      188355 :   u = 0;
      47             : 
      48             :   /* compute columns */
      49     5207530 :   for (ix = 0; ix < a->used; ix++) {
      50             :     /* compute product and carry sum for this term */
      51     5019175 :     r       = ((mp_word) u) + ((mp_word)*tmpa++) * ((mp_word)b);
      52             : 
      53             :     /* mask off higher bits to get a single digit */
      54     5019175 :     *tmpc++ = (mp_digit) (r & ((mp_word) MP_MASK));
      55             : 
      56             :     /* send carry into next iteration */
      57     5019175 :     u       = (mp_digit) (r >> ((mp_word) DIGIT_BIT));
      58             :   }
      59             : 
      60             :   /* store final carry [if any] and increment ix offset  */
      61      188355 :   *tmpc++ = u;
      62      188355 :   ++ix;
      63             : 
      64             :   /* now zero digits above the top */
      65      376710 :   while (ix++ < olduse) {
      66           0 :      *tmpc++ = 0;
      67             :   }
      68             : 
      69             :   /* set used count */
      70      188355 :   c->used = a->used + 1;
      71      188355 :   mp_clamp(c);
      72             : 
      73      188355 :   return MP_OKAY;
      74             : }
      75             : #endif
      76             : 
      77             : /* $Source: /cvs/libtom/libtommath/bn_mp_mul_d.c,v $ */
      78             : /* $Revision: 1.4 $ */
      79             : /* $Date: 2006/12/28 01:25:13 $ */