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authorJakub Jelinek <jakub@redhat.com>2007-07-12 18:26:36 +0000
committerJakub Jelinek <jakub@redhat.com>2007-07-12 18:26:36 +0000
commit0ecb606cb6cf65de1d9fc8a919bceb4be476c602 (patch)
tree2ea1f8305970753e4a657acb2ccc15ca3eec8e2c /stdlib/rshift.c
parent7d58530341304d403a6626d7f7a1913165fe2f32 (diff)
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2.5-18.1
Diffstat (limited to 'stdlib/rshift.c')
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1 files changed, 88 insertions, 0 deletions
diff --git a/stdlib/rshift.c b/stdlib/rshift.c
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+/* mpn_rshift -- Shift right a low-level natural-number integer.
+
+Copyright (C) 1991, 1993, 1994, 1996 Free Software Foundation, Inc.
+
+This file is part of the GNU MP Library.
+
+The GNU MP Library is free software; you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation; either version 2.1 of the License, or (at your
+option) any later version.
+
+The GNU MP Library is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+License for more details.
+
+You should have received a copy of the GNU Lesser General Public License
+along with the GNU MP Library; see the file COPYING.LIB. If not, write to
+the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+MA 02111-1307, USA. */
+
+#include <gmp.h>
+#include "gmp-impl.h"
+
+/* Shift U (pointed to by UP and USIZE limbs long) CNT bits to the right
+ and store the USIZE least significant limbs of the result at WP.
+ The bits shifted out to the right are returned.
+
+ Argument constraints:
+ 1. 0 < CNT < BITS_PER_MP_LIMB
+ 2. If the result is to be written over the input, WP must be <= UP.
+*/
+
+mp_limb_t
+#if __STDC__
+mpn_rshift (register mp_ptr wp,
+ register mp_srcptr up, mp_size_t usize,
+ register unsigned int cnt)
+#else
+mpn_rshift (wp, up, usize, cnt)
+ register mp_ptr wp;
+ register mp_srcptr up;
+ mp_size_t usize;
+ register unsigned int cnt;
+#endif
+{
+ register mp_limb_t high_limb, low_limb;
+ register unsigned sh_1, sh_2;
+ register mp_size_t i;
+ mp_limb_t retval;
+
+#ifdef DEBUG
+ if (usize == 0 || cnt == 0)
+ abort ();
+#endif
+
+ sh_1 = cnt;
+
+#if 0
+ if (sh_1 == 0)
+ {
+ if (wp != up)
+ {
+ /* Copy from low end to high end, to allow specified input/output
+ overlapping. */
+ for (i = 0; i < usize; i++)
+ wp[i] = up[i];
+ }
+ return usize;
+ }
+#endif
+
+ wp -= 1;
+ sh_2 = BITS_PER_MP_LIMB - sh_1;
+ high_limb = up[0];
+ retval = high_limb << sh_2;
+ low_limb = high_limb;
+
+ for (i = 1; i < usize; i++)
+ {
+ high_limb = up[i];
+ wp[i] = (low_limb >> sh_1) | (high_limb << sh_2);
+ low_limb = high_limb;
+ }
+ wp[i] = low_limb >> sh_1;
+
+ return retval;
+}