+
+ m4_ifdef([gl_FUNC_LOG_IEEE], [
+ if test $gl_log_required = ieee && test $REPLACE_LOG = 0; then
+ AC_CACHE_CHECK([whether log works according to ISO C 99 with IEC 60559],
+ [gl_cv_func_log_ieee],
+ [
+ save_LIBS="$LIBS"
+ LIBS="$LIBS $LOG_LIBM"
+ AC_RUN_IFELSE(
+ [AC_LANG_SOURCE([[
+#ifndef __NO_MATH_INLINES
+# define __NO_MATH_INLINES 1 /* for glibc */
+#endif
+#include <math.h>
+/* Compare two numbers with ==.
+ This is a separate function because IRIX 6.5 "cc -O" miscompiles an
+ 'x == x' test. */
+static int
+numeric_equal (double x, double y)
+{
+ return x == y;
+}
+static double dummy (double x) { return 0; }
+int main (int argc, char *argv[])
+{
+ double (*my_log) (double) = argc ? log : dummy;
+ /* Test log(negative).
+ This test fails on NetBSD 5.1, Solaris 11 2011-11. */
+ double y = my_log (-1.0);
+ if (numeric_equal (y, y))
+ return 1;
+ return 0;
+}
+ ]])],
+ [gl_cv_func_log_ieee=yes],
+ [gl_cv_func_log_ieee=no],
+ [gl_cv_func_log_ieee="guessing no"])
+ LIBS="$save_LIBS"
+ ])
+ case "$gl_cv_func_log_ieee" in
+ *yes) ;;
+ *) REPLACE_LOG=1 ;;
+ esac
+ fi
+ ])