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diff --git a/m4/isinf.m4 b/m4/isinf.m4
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+# isinf.m4 serial 3
+dnl Copyright (C) 2007-2010 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_ISINF],
+[
+ AC_REQUIRE([gl_MATH_H_DEFAULTS])
+ dnl Persuade glibc <math.h> to declare isinf.
+ AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
+ AC_CHECK_DECLS([isinf], , , [#include <math.h>])
+ if test "$ac_cv_have_decl_isinf" = yes; then
+ gl_CHECK_MATH_LIB([ISINF_LIBM], [x = isinf (x);])
+ if test "$ISINF_LIBM" != missing; then
+ dnl Test whether isinf() on 'long double' works.
+ gl_ISINFL_WORKS
+ case "$gl_cv_func_isinfl_works" in
+ *yes) ;;
+ *) ISINF_LIBM=missing;;
+ esac
+ fi
+ fi
+ if test "$ac_cv_have_decl_isinf" != yes ||
+ test "$ISINF_LIBM" = missing; then
+ REPLACE_ISINF=1
+ AC_LIBOBJ([isinf])
+ ISINF_LIBM=
+ fi
+ AC_SUBST([ISINF_LIBM])
+])
+
+dnl Test whether isinf() correctly returns false for LDBL_MAX.
+AC_DEFUN([gl_ISINFL_WORKS],
+[
+ AC_REQUIRE([AC_PROG_CC])
+ AC_REQUIRE([gl_BIGENDIAN])
+ AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
+ AC_CACHE_CHECK([whether isinf(long double) works], [gl_cv_func_isinfl_works],
+ [
+ AC_RUN_IFELSE([AC_LANG_PROGRAM([[#include <float.h>
+ #include <math.h>]],
+ [[return !!isinf(LDBL_MAX);]])],
+ [gl_cv_func_isinfl_works=yes],
+ [gl_cv_func_isinfl_works=no],
+ [gl_cv_func_isinfl_works="guessing no"])
+ ])
+])