Fix formula.

[gnulib.git] / m4 / isnan.m4

diff --git a/m4/isnan.m4 b/m4/isnan.m4
index f065a50..d4729cd 100644 (file)
--- a/m4/isnan.m4
+++ b/m4/isnan.m4
@@ -8,12 +8,18 @@ dnl Check how to get or define isnan() without linking with libm.
 
 AC_DEFUN([gl_FUNC_ISNAN_NO_LIBM],
 [
-  AC_CHECK_FUNC([isnan],
-    [gl_cv_func_isnan_no_libm=yes],
-    [gl_cv_func_isnan_no_libm=no])
+  AC_CACHE_CHECK([whether isnan(double) can be used without linking with libm],
+    [gl_cv_func_isnan_no_libm],
+    [
+      AC_TRY_LINK([#include <math.h>
+                   double x;],
+                  [return isnan (x);],
+        [gl_cv_func_isnan_no_libm=yes],
+        [gl_cv_func_isnan_no_libm=no])
+    ])
   if test $gl_cv_func_isnan_no_libm = yes; then
     AC_DEFINE([HAVE_ISNAN_IN_LIBC], 1,
-      [Define if the isnan() function is available in libc.])
+      [Define if the isnan(double) function is available in libc.])
   else
     AC_LIBOBJ([isnan])
     gl_DOUBLE_EXPONENT_LOCATION
@@ -92,14 +98,17 @@ int main ()
         [gl_cv_cc_double_expbit0=`cat conftest.out`],
         [gl_cv_cc_double_expbit0="unknown"],
         [
-          dnl On ARM, integer types are stored in little-endian byte order,
-          dnl but floats are stored in big-endian word order.
+          dnl On ARM, there are two 'double' floating-point formats, used by
+          dnl different sets of instructions: The older FPA instructions assume
+          dnl that they are stored in big-endian word order, while the words
+          dnl (like integer types) are stored in little-endian byte order.
+          dnl The newer VFP instructions assume little-endian order consistenly.
           AC_EGREP_CPP([mixed_endianness], [
 #if defined arm || defined __arm || defined __arm__
   mixed_endianness
 #endif
             ],
-            [gl_cv_cc_double_expbit0="word 0 bit 20"],
+            [gl_cv_cc_double_expbit0="unknown"],
             [
               AC_C_BIGENDIAN(
                 [gl_cv_cc_double_expbit0="word 0 bit 20"],