1  /* mpn_lshift -- Shift left low level.
       2  
       3  Copyright (C) 1991, 1993, 1994, 1996 Free Software Foundation, Inc.
       4  
       5  This file is part of the GNU MP Library.
       6  
       7  The GNU MP Library is free software; you can redistribute it and/or modify
       8  it under the terms of the GNU Lesser General Public License as published by
       9  the Free Software Foundation; either version 2.1 of the License, or (at your
      10  option) any later version.
      11  
      12  The GNU MP Library is distributed in the hope that it will be useful, but
      13  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
      14  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
      15  License for more details.
      16  
      17  You should have received a copy of the GNU Lesser General Public License
      18  along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
      19  the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
      20  MA 02111-1307, USA. */
      21  
      22  #include <config.h>
      23  #include "gmp-impl.h"
      24  
      25  /* Shift U (pointed to by UP and USIZE digits long) CNT bits to the left
      26     and store the USIZE least significant digits of the result at WP.
      27     Return the bits shifted out from the most significant digit.
      28  
      29     Argument constraints:
      30     1. 0 < CNT < BITS_PER_MP_LIMB
      31     2. If the result is to be written over the input, WP must be >= UP.
      32  */
      33  
      34  mp_limb_t
      35  #if __STDC__
      36  mpn_lshift (register mp_ptr wp,
      37  	    register mp_srcptr up, mp_size_t usize,
      38  	    register unsigned int cnt)
      39  #else
      40  mpn_lshift (wp, up, usize, cnt)
      41       register mp_ptr wp;
      42       register mp_srcptr up;
      43       mp_size_t usize;
      44       register unsigned int cnt;
      45  #endif
      46  {
      47    register mp_limb_t high_limb, low_limb;
      48    register unsigned sh_1, sh_2;
      49    register mp_size_t i;
      50    mp_limb_t retval;
      51  
      52  #ifdef DEBUG
      53    if (usize == 0 || cnt == 0)
      54      abort ();
      55  #endif
      56  
      57    sh_1 = cnt;
      58  #if 0
      59    if (sh_1 == 0)
      60      {
      61        if (wp != up)
      62  	{
      63  	  /* Copy from high end to low end, to allow specified input/output
      64  	     overlapping.  */
      65  	  for (i = usize - 1; i >= 0; i--)
      66  	    wp[i] = up[i];
      67  	}
      68        return 0;
      69      }
      70  #endif
      71  
      72    wp += 1;
      73    sh_2 = BITS_PER_MP_LIMB - sh_1;
      74    i = usize - 1;
      75    low_limb = up[i];
      76    retval = low_limb >> sh_2;
      77    high_limb = low_limb;
      78    while (--i >= 0)
      79      {
      80        low_limb = up[i];
      81        wp[i] = (high_limb << sh_1) | (low_limb >> sh_2);
      82        high_limb = low_limb;
      83      }
      84    wp[i] = high_limb << sh_1;
      85  
      86    return retval;
      87  }