--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2011-10-14  Bruno Haible  <bruno@clisp.org>
+
+	New module 'integer_length_l'.
+	* lib/integer_length_l.c: New file.
+	* modules/integer_length_l: New file.
+
 2011-10-14  Bruno Haible  <bruno@clisp.org>
 
 	Tests for module 'integer_length'.

new file mode 100644
--- /dev/null
+++ b/lib/integer_length_l.c
@@ -0,0 +1,81 @@
+/* integer_length_l - find most significant bit in an 'unsigned long'.
+   Copyright (C) 2011 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/>.  */
+
+/* Written by Bruno Haible <bruno@clisp.org>, 2011.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include "integer_length.h"
+
+#include <limits.h>
+#include <stddef.h>
+
+#undef MIN
+#define MIN(a,b) ((a) < (b) ? (a) : (b))
+
+#ifdef USE_LONG_LONG
+# define FUNC integer_length_ll
+# define TYPE unsigned long long
+# define GCC_BUILTIN __builtin_clzll
+#else
+# define FUNC integer_length_l
+# define TYPE unsigned long
+# define GCC_BUILTIN __builtin_clzl
+#endif
+
+#define NBITS (sizeof (TYPE) * CHAR_BIT)
+
+/* Modify shift count to be in bounds, even in dead code, otherwise GCC
+   emits warnings "right shift count >= width of type".  */
+#define MSC(i) MIN (i, NBITS - 1)
+
+int
+FUNC (TYPE x)
+{
+#if __GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4)
+  if (x == 0)
+    return 0;
+  else
+    return NBITS - GCC_BUILTIN (x);
+#else
+  /* Split x into chunks, and look at one chunk after the other.  */
+  if (sizeof (TYPE) > 2 * sizeof (unsigned int))
+    {
+      /* Generic loop.  */
+      size_t i;
+
+      for (i = (sizeof (TYPE) - 1) / sizeof (unsigned int); i >= 2; i--)
+        {
+          unsigned int y = x >> (i * sizeof (unsigned int) * CHAR_BIT);
+          if (y != 0)
+            return i * sizeof (unsigned int) * CHAR_BIT + integer_length (y);
+        }
+    }
+
+  /* Unrolled the last 2 loop rounds.  */
+  /* i = 1 */
+  if (sizeof (TYPE) > 1 * sizeof (unsigned int))
+    {
+      unsigned int y = x >> MSC (1 * sizeof (unsigned int) * CHAR_BIT);
+      if (y != 0)
+        return 1 * sizeof (unsigned int) * CHAR_BIT + integer_length (y);
+    }
+
+  /* i = 0 */
+  return integer_length ((unsigned int) x);
+#endif
+}

new file mode 100644
--- /dev/null
+++ b/modules/integer_length_l
@@ -0,0 +1,25 @@
+Description:
+Finds the most significant bit in an 'unsigned long'.
+
+Files:
+lib/integer_length.h
+lib/integer_length_l.c
+m4/longlong.m4
+
+Depends-on:
+integer_length
+
+configure.ac:
+AC_REQUIRE([AC_TYPE_UNSIGNED_LONG_LONG_INT])
+
+Makefile.am:
+lib_SOURCES += integer_length_l.c
+
+Include:
+"integer_length.h"
+
+License:
+LGPLv2+
+
+Maintainer:
+Bruno Haible