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# logb.m4 serial 6
dnl Copyright (C) 2010-2014 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_LOGB],
[
AC_REQUIRE([gl_MATH_H_DEFAULTS])
dnl Persuade glibc <math.h> to declare logb().
AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
dnl Test whether logb() is declared.
AC_CHECK_DECLS([logb], , , [[#include <math.h>]])
if test "$ac_cv_have_decl_logb" != yes; then
HAVE_DECL_LOGB=0
fi
dnl Test whether logb() can be used without libm.
LOGB_LIBM=?
AC_LINK_IFELSE(
[AC_LANG_PROGRAM(
[[#ifndef __NO_MATH_INLINES
# define __NO_MATH_INLINES 1 /* for glibc */
#endif
#include <math.h>
extern
#ifdef __cplusplus
"C"
#endif
double logb (double x);
double x;]],
[[x = logb(x);]])],
[LOGB_LIBM=])
if test "$LOGB_LIBM" = "?"; then
save_LIBS="$LIBS"
LIBS="$LIBS -lm"
AC_LINK_IFELSE(
[AC_LANG_PROGRAM(
[[#ifndef __NO_MATH_INLINES
# define __NO_MATH_INLINES 1 /* for glibc */
#endif
#include <math.h>
extern
#ifdef __cplusplus
"C"
#endif
double logb (double x);
double x;]],
[[x = logb(x);]])],
[LOGB_LIBM="-lm"])
LIBS="$save_LIBS"
fi
if test "$LOGB_LIBM" != "?"; then
HAVE_LOGB=1
save_LIBS="$LIBS"
LIBS="$LIBS $LOGB_LIBM"
gl_FUNC_LOGB_WORKS
LIBS="$save_LIBS"
case "$gl_cv_func_logb_works" in
*yes) ;;
*) REPLACE_LOGB=1 ;;
esac
else
HAVE_LOGB=0
fi
if test $HAVE_LOGB = 0 || test $REPLACE_LOGB = 1; then
dnl Find libraries needed to link lib/logb.c.
AC_REQUIRE([gl_FUNC_FREXP])
AC_REQUIRE([gl_FUNC_ISNAND])
LOGB_LIBM=
dnl Append $FREXP_LIBM to LOGB_LIBM, avoiding gratuitous duplicates.
case " $LOGB_LIBM " in
*" $FREXP_LIBM "*) ;;
*) LOGB_LIBM="$LOGB_LIBM $FREXP_LIBM" ;;
esac
dnl Append $ISNAND_LIBM to LOGB_LIBM, avoiding gratuitous duplicates.
case " $LOGB_LIBM " in
*" $ISNAND_LIBM "*) ;;
*) LOGB_LIBM="$LOGB_LIBM $ISNAND_LIBM" ;;
esac
fi
AC_SUBST([LOGB_LIBM])
])
dnl Test whether logb() works.
dnl On glibc 2.11/ppc, glibc 2.7/sparc, glibc 2.7/hppa, Solaris 10/SPARC,
dnl Cygwin 1.5.x, the return value for subnormal (denormalized) arguments is
dnl too large.
AC_DEFUN([gl_FUNC_LOGB_WORKS],
[
AC_REQUIRE([AC_PROG_CC])
AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
AC_CACHE_CHECK([whether logb works], [gl_cv_func_logb_works],
[
AC_RUN_IFELSE(
[AC_LANG_SOURCE([[
#include <float.h>
#include <math.h>
extern
#ifdef __cplusplus
"C"
#endif
double logb (double);
volatile double x;
int main ()
{
int i;
for (i = 1, x = 1.0; i >= DBL_MIN_EXP; i--, x *= 0.5)
;
/* Here i = DBL_MIN_EXP - 1. Either x = 2^(i-1) is subnormal or x = 0.0. */
if (x > 0.0 && !(logb (x) == (double)(i - 1)))
return 1;
return 0;
}
]])],
[gl_cv_func_logb_works=yes],
[gl_cv_func_logb_works=no],
[case "$host_os" in
*gnu* | solaris* | cygwin*) gl_cv_func_logb_works="guessing no";;
*) gl_cv_func_logb_works="guessing yes";;
esac
])
])
])
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