New module 'ilogb'.

* lib/math.in.h (ilogb): New declaration.
* lib/ilogb.c: New file.
* m4/ilogb.m4: New file.
* m4/math_h.m4 (gl_MATH_H): Test whether ilogb is declared.
(gl_MATH_H_DEFAULTS): Initialize GNULIB_ILOGB, HAVE_ILOGB,
REPLACE_ILOGB.
* modules/math (Makefile.am): Substitute GNULIB_ILOGB, HAVE_ILOGB,
REPLACE_ILOGB.
* modules/ilogb: New file.
* tests/test-math-c++.cc: Check the declaration of ilogb.
* doc/posix-functions/ilogb.texi: Mention the new module.

1 files changed, 68 insertions, 0 deletions

diff --git a/lib/ilogb.c b/lib/ilogb.c
new file mode 100644
index 0000000000..2b92a08890
--- /dev/null
+++ b/lib/ilogb.c
@@ -0,0 +1,68 @@
+/* Floating-point exponent.
+   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/>.  */
+
+#if ! (defined USE_LONG_DOUBLE || defined USE_FLOAT)
+# include <config.h>
+#endif
+
+/* Specification.  */
+#include <math.h>
+
+#include <limits.h>
+
+#ifdef USE_LONG_DOUBLE
+# define ILOGB ilogbl
+# define DOUBLE long double
+# define L_(literal) literal##L
+# define FREXP frexpl
+# define ISNAN isnanl
+#elif ! defined USE_FLOAT
+# define ILOGB ilogb
+# define DOUBLE double
+# define L_(literal) literal
+# define FREXP frexp
+# define ISNAN isnand
+#else /* defined USE_FLOAT */
+# define ILOGB ilogbf
+# define DOUBLE float
+# define L_(literal) literal##f
+# define FREXP frexpf
+# define ISNAN isnanf
+#endif
+
+int
+ILOGB (DOUBLE x)
+{
+  if (isfinite (x))
+    {
+      if (x == L_(0.0))
+        return FP_ILOGB0;
+      else
+        {
+          int e;
+
+          (void) FREXP (x, &e);
+          return e - 1;
+        }
+    }
+  else
+    {
+      if (ISNAN (x))
+        return FP_ILOGBNAN;
+      else
+        return INT_MAX;
+    }
+}