crypto/external/bsd/heimdal/dist/lib/hcrypto/libtommath/bn_mp_lshd.c

   1 /*      $NetBSD: bn_mp_lshd.c,v 1.1.1.2 2014/04/24 12:45:31 pettai Exp $        */
   2
   3 #include <tommath.h>
   4 #ifdef BN_MP_LSHD_C
   5 /* LibTomMath, multiple-precision integer library -- Tom St Denis
   6  *
   7  * LibTomMath is a library that provides multiple-precision
   8  * integer arithmetic as well as number theoretic functionality.
   9  *
  10  * The library was designed directly after the MPI library by
  11  * Michael Fromberger but has been written from scratch with
  12  * additional optimizations in place.
  13  *
  14  * The library is free for all purposes without any express
  15  * guarantee it works.
  16  *
  17  * Tom St Denis, tomstdenis@gmail.com, http://libtom.org
  18  */
  19
  20 /* shift left a certain amount of digits */
  21 int mp_lshd (mp_int * a, int b)
  22 {
  23   int     x, res;
  24
  25   /* if its less than zero return */
  26   if (b <= 0) {
  27     return MP_OKAY;
  28   }
  29
  30   /* grow to fit the new digits */
  31   if (a->alloc < a->used + b) {
  32      if ((res = mp_grow (a, a->used + b)) != MP_OKAY) {
  33        return res;
  34      }
  35   }
  36
  37   {
  38     register mp_digit *top, *bottom;
  39
  40     /* increment the used by the shift amount then copy upwards */
  41     a->used += b;
  42
  43     /* top */
  44     top = a->dp + a->used - 1;
  45
  46     /* base */
  47     bottom = a->dp + a->used - 1 - b;
  48
  49     /* much like mp_rshd this is implemented using a sliding window
  50      * except the window goes the otherway around.  Copying from
  51      * the bottom to the top.  see bn_mp_rshd.c for more info.
  52      */
  53     for (x = a->used - 1; x >= b; x--) {
  54       *top-- = *bottom--;
  55     }
  56
  57     /* zero the lower digits */
  58     top = a->dp;
  59     for (x = 0; x < b; x++) {
  60       *top++ = 0;
  61     }
  62   }
  63   return MP_OKAY;
  64 }
  65 #endif
  66
  67 /* Source: /cvs/libtom/libtommath/bn_mp_lshd.c,v  */
  68 /* Revision: 1.4  */
  69 /* Date: 2006/12/28 01:25:13  */