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      1 #include <tommath.h>
      2 #ifdef BN_MP_LSHD_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 a certain amount of digits */
     19 int mp_lshd (mp_int * a, int b)
     20 {
     21   int     x, res;
     22 
     23   /* if its less than zero return */
     24   if (b <= 0) {
     25     return MP_OKAY;
     26   }
     27 
     28   /* grow to fit the new digits */
     29   if (a->alloc < a->used + b) {
     30      if ((res = mp_grow (a, a->used + b)) != MP_OKAY) {
     31        return res;
     32      }
     33   }
     34 
     35   {
     36     register mp_digit *top, *bottom;
     37 
     38     /* increment the used by the shift amount then copy upwards */
     39     a->used += b;
     40 
     41     /* top */
     42     top = a->dp + a->used - 1;
     43 
     44     /* base */
     45     bottom = a->dp + a->used - 1 - b;
     46 
     47     /* much like mp_rshd this is implemented using a sliding window
     48      * except the window goes the otherway around.  Copying from
     49      * the bottom to the top.  see bn_mp_rshd.c for more info.
     50      */
     51     for (x = a->used - 1; x >= b; x--) {
     52       *top-- = *bottom--;
     53     }
     54 
     55     /* zero the lower digits */
     56     top = a->dp;
     57     for (x = 0; x < b; x++) {
     58       *top++ = 0;
     59     }
     60   }
     61   return MP_OKAY;
     62 }
     63 #endif
     64 
     65 /* $Source: /cvs/libtom/libtommath/bn_mp_lshd.c,v $ */
     66 /* $Revision: 1.3 $ */
     67 /* $Date: 2006/03/31 14:18:44 $ */
     68