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Annotation of OpenXM_contrib/gmp/mpn/generic/rshift.c, Revision 1.1.1.1

1.1       maekawa     1: /* mpn_rshift -- Shift right a low-level natural-number integer.
                      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 Library General Public License as published by
                      9: the Free Software Foundation; either version 2 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 Library General Public
                     15: License for more details.
                     16:
                     17: You should have received a copy of the GNU Library 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 "gmp.h"
                     23: #include "gmp-impl.h"
                     24:
                     25: /* Shift U (pointed to by UP and USIZE limbs long) CNT bits to the right
                     26:    and store the USIZE least significant limbs of the result at WP.
                     27:    The bits shifted out to the right are returned.
                     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_rshift (register mp_ptr wp,
                     37:            register mp_srcptr up, mp_size_t usize,
                     38:            register unsigned int cnt)
                     39: #else
                     40: mpn_rshift (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:
                     59: #if 0
                     60:   if (sh_1 == 0)
                     61:     {
                     62:       if (wp != up)
                     63:        {
                     64:          /* Copy from low end to high end, to allow specified input/output
                     65:             overlapping.  */
                     66:          for (i = 0; i < usize; i++)
                     67:            wp[i] = up[i];
                     68:        }
                     69:       return usize;
                     70:     }
                     71: #endif
                     72:
                     73:   wp -= 1;
                     74:   sh_2 = BITS_PER_MP_LIMB - sh_1;
                     75:   high_limb = up[0];
                     76:   retval = high_limb << sh_2;
                     77:   low_limb = high_limb;
                     78:
                     79:   for (i = 1; i < usize; i++)
                     80:     {
                     81:       high_limb = up[i];
                     82:       wp[i] = (low_limb >> sh_1) | (high_limb << sh_2);
                     83:       low_limb = high_limb;
                     84:     }
                     85:   wp[i] = low_limb >> sh_1;
                     86:
                     87:   return retval;
                     88: }