modf-ieee: Work around test failures on *BSD, IRIX, OSF/1, Cygwin.

* m4/modf-ieee.m4: New file.
* m4/modf.m4 (gl_FUNC_MODF): If gl_FUNC_MODF_IEEE is present, test
whether modf works with NaN and Inf. Replace it if not.
* lib/math.in.h (modf): New declaration.
* lib/modf.c: New file.
* m4/math_h.m4 (gl_MATH_H): Test whether modf is declared.
(gl_MATH_H_DEFAULTS): Initialize GNULIB_MODF, REPLACE_MODF.
* modules/math (Makefile.am): Substitute GNULIB_MODF, REPLACE_MODF.
* modules/modf (Files): Add lib/modf.c.
(Depends-on): Add math, isfinite, trunc, isinf.
(configure.ac): Addrange to compile lib/modf.c if needed.
* modules/modf-ieee (Files): Add m4/modf-ieee.m4, m4/minus-zero.m4,
m4/signbit.m4.
(configure.ac): Invoke gl_FUNC_MODF_IEEE.
* tests/test-math-c++.cc: Check the declaration of modf.
* doc/posix-functions/modf.texi: Mention the modf-ieee module.

1 files changed, 44 insertions, 0 deletions

diff --git a/lib/modf.c b/lib/modf.c
new file mode 100644
index 0000000000..19989e5b8d
--- /dev/null
+++ b/lib/modf.c
@@ -0,0 +1,44 @@
+/* Get signed integer and fractional parts of a floating-point number.
+   Copyright (C) 2012 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 3 of the License, 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, see <http://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include <math.h>
+
+double
+modf (double x, double *iptr)
+{
+  if (isfinite (x))
+    {
+      double integer_part = trunc (x);
+      *iptr = integer_part;
+      return x - integer_part;
+    }
+  else
+    {
+      if (isinf (x))
+        {
+          *iptr = x;
+          return 1.0 / x;
+        }
+      else /* isnand (x) */
+        {
+          *iptr = x;
+          return x;
+        }
+    }
+}