Libvirt wants to use ffs() to avoid dragging in -lm for log2().
* modules/ffs: New file.
* m4/ffs.m4: Likewise.
* lib/ffs.c: Likewise.
* m4/strings_h.m4 (gl_HEADER_STRINGS_H_DEFAULTS): Add default.
* modules/strings (Makefile.am): Substitute witness.
(Depends-on): Add c++defs.
* lib/strings.in.h (ffs): Declare.
* modules/ffs-tests: New test file.
* tests/test-ffs.c: Test new module.
* MODULES.html.sh (Integer arithmetic functions): Mention it.
* doc/posix-functions/ffs.texi (ffs): Likewise.
Signed-off-by: Eric Blake <eblake@redhat.com>
2011-07-11 Eric Blake <eblake@redhat.com>
+ ffs: new module
+ * modules/ffs: New file.
+ * m4/ffs.m4: Likewise.
+ * lib/ffs.c: Likewise.
+ * m4/strings_h.m4 (gl_HEADER_STRINGS_H_DEFAULTS): Add default.
+ * modules/strings (Makefile.am): Substitute witness.
+ (Depends-on): Add c++defs.
+ * lib/strings.in.h (ffs): Declare.
+ * modules/ffs-tests: New test file.
+ * tests/test-ffs.c: Test new module.
+ * MODULES.html.sh (Integer arithmetic functions): Mention it.
+ * doc/posix-functions/ffs.texi (ffs): Likewise.
+
regex: avoid compiler warning
* lib/regex.c (includes): Include <strings.h>, for use of
strcasecmp in regcomp.c.
func_begin_table
func_module count-one-bits
+ func_module ffs
func_module gcd
func_module minmax
func_end_table
POSIX specification:@* @url{http://www.opengroup.org/onlinepubs/9699919799/functions/ffs.html}
-Gnulib module: ---
+Gnulib module: ffs
Portability problems fixed by Gnulib:
@itemize
+@item
+This function is missing on some platforms:
+mingw.
@end itemize
Portability problems not fixed by Gnulib:
@itemize
-@item
-This function is missing on some platforms:
-mingw.
@end itemize
--- /dev/null
+/* ffs.c -- find the first set bit in a word.
+ Copyright (C) 2011 Free Software Foundation, Inc.
+
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 3 of the License, or
+ (at your option) any later version.
+
+ This program 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 General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <http://www.gnu.org/licenses/>. */
+
+/* Written by Eric Blake. */
+
+#include <strings.h>
+
+int
+ffs (int i)
+{
+#if __GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4)
+ return __builtin_ffs (i);
+#else
+ /* http://graphics.stanford.edu/~seander/bithacks.html#ZerosOnRightMultLookup
+ gives this deBruijn constant for a branch-less computation, although
+ that table counted trailing zeros rather than bit position. */
+ static unsigned int table[] = {
+ 1, 2, 29, 3, 30, 15, 25, 4, 31, 23, 21, 16, 26, 18, 5, 9,
+ 32, 28, 14, 24, 22, 20, 17, 8, 27, 13, 19, 7, 12, 6, 11, 10
+ };
+ unsigned int u = i;
+ unsigned int bit = u & -u;
+ return table[(bit * 0x077cb531U) >> 27] - !i;
+#endif
+}
#define _@GUARD_PREFIX@_STRINGS_H
+/* The definitions of _GL_FUNCDECL_RPL etc. are copied here. */
+
/* The definition of _GL_ARG_NONNULL is copied here. */
/* The definition of _GL_WARN_ON_USE is copied here. */
#endif
+ /* Find the index of the least-significant set bit. */
+#if @GNULIB_FFS@
+# if !@HAVE_FFS@
+_GL_FUNCDECL_SYS (ffs, int, (int i));
+# endif
+_GL_CXXALIAS_SYS (ffs, int, (int i));
+_GL_CXXALIASWARN (ffs);
+#elif defined GNULIB_POSIXCHECK
+# undef ffs
+# if HAVE_RAW_DECL_FFS
+_GL_WARN_ON_USE (ffs, "ffs is not portable - use the ffs module");
+# endif
+#endif
+
/* Compare strings S1 and S2, ignoring case, returning less than, equal to or
greater than zero if S1 is lexicographically less than, equal to or greater
than S2.
--- /dev/null
+# ffs.m4 serial 1
+dnl Copyright (C) 2011 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+AC_DEFUN([gl_FUNC_FFS],
+[
+ AC_CHECK_FUNCS_ONCE([ffs])
+ if test $ac_cv_func_ffs = no; then
+ HAVE_FFS=0
+ fi
+])
-# Configure a replacement for <string.h>.
-# serial 3
+# Configure a replacement for <strings.h>.
+# serial 4
# Copyright (C) 2007, 2009-2011 Free Software Foundation, Inc.
# This file is free software; the Free Software Foundation
dnl Check for declarations of anything we want to poison if the
dnl corresponding gnulib module is not in use.
gl_WARN_ON_USE_PREPARE([[#include <strings.h>
- ]], [strcasecmp strncasecmp])
+ ]], [ffs strcasecmp strncasecmp])
])
AC_DEFUN([gl_STRINGS_MODULE_INDICATOR],
AC_DEFUN([gl_HEADER_STRINGS_H_DEFAULTS],
[
+ GNULIB_FFS=0; AC_SUBST([GNULIB_FFS])
dnl Assume proper GNU behavior unless another module says otherwise.
+ HAVE_FFS=1; AC_SUBST([HAVE_FFS])
HAVE_STRCASECMP=1; AC_SUBST([HAVE_STRCASECMP])
HAVE_DECL_STRNCASECMP=1; AC_SUBST([HAVE_DECL_STRNCASECMP])
])
--- /dev/null
+Description:
+Finds the index of the least-significant set bit.
+
+Files:
+lib/ffs.c
+m4/ffs.m4
+
+Depends-on:
+strings
+
+configure.ac:
+gl_FUNC_FFS
+if test $HAVE_FFS = 0; then
+ AC_LIBOBJ([ffs])
+fi
+gl_STRINGS_MODULE_INDICATOR([ffs])
+
+Makefile.am:
+
+Include:
+<strings.h>
+
+License:
+LGPLv2+
+
+Maintainer:
+Eric Blake
--- /dev/null
+Files:
+tests/test-ffs.c
+tests/macros.h
+tests/signature.h
+
+Depends-on:
+
+configure.ac:
+
+Makefile.am:
+TESTS += test-ffs
+check_PROGRAMS += test-ffs
Depends-on:
arg-nonnull
+c++defs
include_next
warn-on-use
# We need the following in order to create <strings.h> when the system
# doesn't have one that works with the given compiler.
-strings.h: strings.in.h $(top_builddir)/config.status $(WARN_ON_USE_H) $(ARG_NONNULL_H)
+strings.h: strings.in.h $(top_builddir)/config.status $(CXXDEFS_H) $(WARN_ON_USE_H) $(ARG_NONNULL_H)
$(AM_V_GEN)rm -f $@-t $@ && \
{ echo '/* DO NOT EDIT! GENERATED AUTOMATICALLY! */' && \
sed -e 's|@''GUARD_PREFIX''@|${gl_include_guard_prefix}|g' \
-e 's|@''PRAGMA_SYSTEM_HEADER''@|@PRAGMA_SYSTEM_HEADER@|g' \
-e 's|@''PRAGMA_COLUMNS''@|@PRAGMA_COLUMNS@|g' \
-e 's|@''NEXT_STRINGS_H''@|$(NEXT_STRINGS_H)|g' \
+ -e 's|@''GNULIB_FFS''@|$(GNULIB_FFS)|g' \
+ -e 's|@''HAVE_FFS''@|$(HAVE_FFS)|g' \
-e 's|@''HAVE_STRCASECMP''@|$(HAVE_STRCASECMP)|g' \
-e 's|@''HAVE_DECL_STRNCASECMP''@|$(HAVE_DECL_STRNCASECMP)|g' \
+ -e '/definitions of _GL_FUNCDECL_RPL/r $(CXXDEFS_H)' \
-e '/definition of _GL_ARG_NONNULL/r $(ARG_NONNULL_H)' \
-e '/definition of _GL_WARN_ON_USE/r $(WARN_ON_USE_H)' \
< $(srcdir)/strings.in.h; \
--- /dev/null
+/*
+ * Copyright (C) 2011 Free Software Foundation, Inc.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>. */
+
+/* Written by Eric Blake. */
+#include <config.h>
+
+#include <strings.h>
+
+#include "signature.h"
+SIGNATURE_CHECK (ffs, int, (int));
+
+#include <limits.h>
+
+#include "macros.h"
+
+static int
+naive (int i)
+{
+ int j;
+ for (j = 0; j < CHAR_BIT * sizeof i; j++)
+ if (i & (1 << j))
+ return j + 1;
+ return 0;
+}
+
+int
+main (int argc, char *argv[])
+{
+ int i;
+
+ for (i = -128; i <= 128; i++)
+ ASSERT (ffs (i) == naive (i));
+ for (i = 0; i < CHAR_BIT * sizeof i; i++)
+ {
+ ASSERT (ffs (1 << i) == naive (1 << i));
+ ASSERT (ffs (1 << i) == i + 1);
+ }
+ return 0;
+}
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