--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2007-02-24  Bruno Haible  <bruno@clisp.org>
+
+	* modules/isnan-nolibm: New file.
+	* lib/isnan.h: New file.
+	* lib/isnan.c: New file.
+	* m4/isnan.m4: New file.
+
 2007-02-24  Bruno Haible  <bruno@clisp.org>
 
 	* lib/frexpl.c (frexpl): Correct return values for x = 1.0L. Don't

new file mode 100644
--- /dev/null
+++ b/lib/isnan.c
@@ -0,0 +1,61 @@
+/* Test for NaN that does not need libm.
+   Copyright (C) 2007 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 2, 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, write to the Free Software Foundation,
+   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
+
+/* Written by Bruno Haible <bruno@clisp.org>, 2007.  */
+
+#include <config.h>
+
+#include <float.h>
+#include <string.h>
+
+#define DBL_EXP_MASK ((DBL_MAX_EXP - DBL_MIN_EXP) | 7)
+
+#define NWORDS \
+  ((sizeof (double) + sizeof (unsigned int) - 1) / sizeof (unsigned int))
+typedef union { double value; unsigned int word[NWORDS]; } memory_double;
+
+int
+rpl_isnan (double x)
+{
+#if defined DBL_EXPBIT0_WORD && defined DBL_EXPBIT0_BIT
+  /* Be careful to not do any floating-point operation on x, such as x == x,
+     because x may be a signaling NaN.  */
+  static memory_double nan = { 0.0 / 0.0 };
+  static double plus_inf = 1.0 / 0.0;
+  static double minus_inf = -1.0 / 0.0;
+  memory_double m;
+
+  /* A NaN can be recognized through its exponent.  But exclude +Infinity and
+     -Infinity, which have the same exponent.  */
+  m.value = x;
+  if ((((m.word[DBL_EXPBIT0_WORD] >> DBL_EXPBIT0_BIT)
+	^ (nan.word[DBL_EXPBIT0_WORD] >> DBL_EXPBIT0_BIT))
+       & DBL_EXP_MASK)
+      == 0)
+    return (memcmp (&m.value, &plus_inf, sizeof (double)) != 0
+	    && memcmp (&m.value, &minus_inf, sizeof (double)) != 0);
+  else
+    return 0;
+#else
+  /* The configuration did not find sufficient information.  Give up about
+     the signaling NaNs, handle only the quiet NaNs.  */
+  if (x == x)
+    return 0;
+  else
+    return 1;
+#endif
+}

new file mode 100644
--- /dev/null
+++ b/lib/isnan.h
@@ -0,0 +1,26 @@
+/* Test for NaN that does not need libm.
+   Copyright (C) 2007 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 2, 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, write to the Free Software Foundation,
+   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
+
+#if HAVE_ISNAN_IN_LIBC
+/* Get declaration of isnan.  */
+# include <math.h>
+#else
+/* Test whether X is a NaN.  */
+# undef isnan
+# define isnan rpl_isnan
+extern int isnan (double x);
+#endif

new file mode 100644
--- /dev/null
+++ b/m4/isnan.m4
@@ -0,0 +1,122 @@
+# isnan.m4 serial 1
+dnl Copyright (C) 2007 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.
+
+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])
+  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.])
+  else
+    AC_LIBOBJ([isnan])
+    gl_DOUBLE_EXPONENT_LOCATION
+  fi
+])
+
+AC_DEFUN([gl_DOUBLE_EXPONENT_LOCATION],
+[
+  AC_CACHE_CHECK([where to find the exponent in a 'double'],
+    [gl_cv_cc_double_expbit0],
+    [
+      AC_TRY_RUN([
+#include <float.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <string.h>
+#define NWORDS \
+  ((sizeof (double) + sizeof (unsigned int) - 1) / sizeof (unsigned int))
+typedef union { double value; unsigned int word[NWORDS]; } memory_double;
+static unsigned int ored_words[NWORDS];
+static unsigned int anded_words[NWORDS];
+static void add_to_ored_words (double x)
+{
+  memory_double m;
+  size_t i;
+  /* Clear it first, in case sizeof (double) < sizeof (memory_double).  */
+  memset (&m, 0, sizeof (memory_double));
+  m.value = x;
+  for (i = 0; i < NWORDS; i++)
+    {
+      ored_words[i] |= m.word[i];
+      anded_words[i] &= m.word[i];
+    }
+}
+int main ()
+{
+  size_t j;
+  FILE *fp = fopen ("conftest.out", "w");
+  if (fp == NULL)
+    return 1;
+  for (j = 0; j < NWORDS; j++)
+    anded_words[j] = ~ (unsigned int) 0;
+  add_to_ored_words (0.25);
+  add_to_ored_words (0.5);
+  add_to_ored_words (1.0);
+  add_to_ored_words (2.0);
+  add_to_ored_words (4.0);
+  /* Remove bits that are common (e.g. if representation of the first mantissa
+     bit is explicit).  */
+  for (j = 0; j < NWORDS; j++)
+    ored_words[j] &= ~anded_words[j];
+  /* Now find the nonzero word.  */
+  for (j = 0; j < NWORDS; j++)
+    if (ored_words[j] != 0)
+      break;
+  if (j < NWORDS)
+    {
+      size_t i;
+      for (i = j + 1; i < NWORDS; i++)
+        if (ored_words[i] != 0)
+          {
+            fprintf (fp, "unknown");
+            return (fclose (fp) != 0);
+          }
+      for (i = 0; ; i++)
+        if ((ored_words[j] >> i) & 1)
+          {
+            fprintf (fp, "word %d bit %d", (int) j, (int) i);
+            return (fclose (fp) != 0);
+          }
+    }
+  fprintf (fp, "unknown");
+  return (fclose (fp) != 0);
+}
+        ],
+        [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.
+          AC_EGREP_CPP([mixed_endianness], [
+#if defined arm || defined __arm || defined __arm__
+  mixed_endianness
+#endif
+            ],
+            [gl_cv_cc_double_expbit0="word 0 bit 20"],
+            [
+              AC_C_BIGENDIAN(
+                [gl_cv_cc_double_expbit0="word 0 bit 20"],
+                [gl_cv_cc_double_expbit0="word 1 bit 20"],
+                [gl_cv_cc_double_expbit0="unknown"])
+            ])
+        ])
+      rm -f conftest.out
+    ])
+  case "$gl_cv_cc_double_expbit0" in
+    word*bit*)
+      word=`echo "$gl_cv_cc_double_expbit0" | sed -e 's/word //' -e 's/ bit.*//'`
+      bit=`echo "$gl_cv_cc_double_expbit0" | sed -e 's/word.*bit //'`
+      AC_DEFINE_UNQUOTED([DBL_EXPBIT0_WORD], [$word],
+        [Define as the word index where to find the exponent of 'double'.])
+      AC_DEFINE_UNQUOTED([DBL_EXPBIT0_BIT], [$bit],
+        [Define as the bit index in the word where to find bit 0 of the exponent of 'double'.])
+      ;;
+  esac
+])

new file mode 100644
--- /dev/null
+++ b/modules/isnan-nolibm
@@ -0,0 +1,24 @@
+Description:
+isnan() function: test for NaN, without requiring libm.
+
+Files:
+lib/isnan.h
+lib/isnan.c
+m4/isnan.m4
+
+Depends-on:
+
+configure.ac:
+gl_FUNC_ISNAN_NO_LIBM
+
+Makefile.am:
+
+Include:
+#include "isnan.h"
+
+License:
+LGPL
+
+Maintainer:
+Bruno Haible
+