glibc/stdlib/rshift.c

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/* mpn_rshift -- Shift right a low-level natural-number integer.
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Copyright (C) 1991-2023 Free Software Foundation, Inc.
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This file is part of the GNU MP Library.
The GNU MP Library is free software; you can redistribute it and/or modify
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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
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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
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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License for more details.
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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, see
Prefer https to http for gnu.org and fsf.org URLs Also, change sources.redhat.com to sourceware.org. This patch was automatically generated by running the following shell script, which uses GNU sed, and which avoids modifying files imported from upstream: sed -ri ' s,(http|ftp)(://(.*\.)?(gnu|fsf|sourceware)\.org($|[^.]|\.[^a-z])),https\2,g s,(http|ftp)(://(.*\.)?)sources\.redhat\.com($|[^.]|\.[^a-z]),https\2sourceware.org\4,g ' \ $(find $(git ls-files) -prune -type f \ ! -name '*.po' \ ! -name 'ChangeLog*' \ ! -path COPYING ! -path COPYING.LIB \ ! -path manual/fdl-1.3.texi ! -path manual/lgpl-2.1.texi \ ! -path manual/texinfo.tex ! -path scripts/config.guess \ ! -path scripts/config.sub ! -path scripts/install-sh \ ! -path scripts/mkinstalldirs ! -path scripts/move-if-change \ ! -path INSTALL ! -path locale/programs/charmap-kw.h \ ! -path po/libc.pot ! -path sysdeps/gnu/errlist.c \ ! '(' -name configure \ -execdir test -f configure.ac -o -f configure.in ';' ')' \ ! '(' -name preconfigure \ -execdir test -f preconfigure.ac ';' ')' \ -print) and then by running 'make dist-prepare' to regenerate files built from the altered files, and then executing the following to cleanup: chmod a+x sysdeps/unix/sysv/linux/riscv/configure # Omit irrelevant whitespace and comment-only changes, # perhaps from a slightly-different Autoconf version. git checkout -f \ sysdeps/csky/configure \ sysdeps/hppa/configure \ sysdeps/riscv/configure \ sysdeps/unix/sysv/linux/csky/configure # Omit changes that caused a pre-commit check to fail like this: # remote: *** error: sysdeps/powerpc/powerpc64/ppc-mcount.S: trailing lines git checkout -f \ sysdeps/powerpc/powerpc64/ppc-mcount.S \ sysdeps/unix/sysv/linux/s390/s390-64/syscall.S # Omit change that caused a pre-commit check to fail like this: # remote: *** error: sysdeps/sparc/sparc64/multiarch/memcpy-ultra3.S: last line does not end in newline git checkout -f sysdeps/sparc/sparc64/multiarch/memcpy-ultra3.S
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<https://www.gnu.org/licenses/>. */
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#include <gmp.h>
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#include "gmp-impl.h"
#include <assert.h>
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/* 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.
*/
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mp_limb_t
mpn_rshift (register mp_ptr wp,
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register mp_srcptr up, mp_size_t usize,
register unsigned int cnt)
{
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register mp_limb_t high_limb, low_limb;
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register unsigned sh_1, sh_2;
register mp_size_t i;
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mp_limb_t retval;
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assert (usize != 0 && cnt != 0);
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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;
}