1/* mpn_rshift -- Shift right a low-level natural-number integer.
2
3Copyright (C) 1991, 1993, 1994, 1996 Free Software Foundation, Inc.
4
5This file is part of the GNU MP Library.
6
7The GNU MP Library is free software; you can redistribute it and/or modify
8it under the terms of the GNU Lesser General Public License as published by
9the Free Software Foundation; either version 2.1 of the License, or (at your
10option) any later version.
11
12The GNU MP Library is distributed in the hope that it will be useful, but
13WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
14or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
15License for more details.
16
17You should have received a copy of the GNU Lesser General Public License
18along with the GNU MP Library; see the file COPYING.LIB. If not, write to
19the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
20MA 02111-1307, USA. */
21
22#include <config.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
34mp_limb_t
35#if __STDC__
36mpn_rshift (register mp_ptr wp,
37 register mp_srcptr up, mp_size_t usize,
38 register unsigned int cnt)
39#else
40mpn_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}
89