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

   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@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 $ */