--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2007-07-22  Ben Pfaff  <blp@gnu.org>
+
+	New module: popcount.
+	* MODULES.html.sh: Add popcount.
+	* modules/popcount: New file.
+	* modules/popcount-tests: New file.
+	* tests/test-popcount.c: New file.
+	* lib/popcount.h: New file.
+	* m4/popcount.m4: New file.
+
 2007-07-22  Paul Eggert  <eggert@cs.ucla.edu>
 
 	* build-aux/announce-gen: Update to GPLv3.

--- a/MODULES.html.sh
+++ b/MODULES.html.sh
@@ -1611,6 +1611,7 @@
   func_begin_table
   func_module gcd
   func_module minmax
+  func_module popcount
   func_end_table
 
   element="Environment variables <stdlib.h>"

new file mode 100644
--- /dev/null
+++ b/lib/popcount.h
@@ -0,0 +1,60 @@
+/* popcount.h -- population count
+   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 Ben Pfaff.  */
+
+#ifndef POPCOUNT_H
+# define POPCOUNT_H 1
+
+#if __GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR >= 4)
+#define POPCOUNT_CALCULATION(NAME)              \
+        return __builtin_##NAME (x);
+#else
+#define POPCOUNT_CALCULATION(NAME)              \
+        int pop;                                \
+        for (pop = 0; x != 0; pop++)            \
+          x &= x - 1;                           \
+        return pop;
+#endif
+
+/* Compute and return the population count of X, that is, the
+   number of 1-bits set in X. */
+static inline int
+popcount (unsigned int x)
+{
+  POPCOUNT_CALCULATION (popcount);
+}
+
+/* Compute and return the population count of X, that is, the
+   number of 1-bits set in X. */
+static inline int
+popcountl (unsigned long int x)
+{
+  POPCOUNT_CALCULATION (popcountl);
+}
+
+#if HAVE_UNSIGNED_LONG_LONG_INT
+/* Compute and return the population count of X, that is, the
+   number of 1-bits set in X. */
+static inline int
+popcountll (unsigned long long int x)
+{
+  POPCOUNT_CALCULATION (popcountll);
+}
+#endif
+
+#endif /* POPCOUNT_H */

new file mode 100644
--- /dev/null
+++ b/m4/popcount.m4
@@ -0,0 +1,12 @@
+# popcount.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.
+
+AC_DEFUN([gl_POPCOUNT],
+[
+  dnl We don't need (and can't compile) popcountll
+  dnl unless the type 'unsigned long long int' exists.
+  AC_REQUIRE([AC_TYPE_UNSIGNED_LONG_LONG_INT])
+])

new file mode 100644
--- /dev/null
+++ b/modules/popcount
@@ -0,0 +1,23 @@
+Description:
+Compute population count (number of 1-bits in a word).
+
+Files:
+lib/popcount.h
+m4/popcount.m4
+
+Depends-on:
+inline
+
+configure.ac:
+gl_POPCOUNT
+
+Makefile.am:
+
+Include:
+"popcount.h"
+
+License:
+GPL
+
+Maintainer:
+Ben Pfaff

new file mode 100644
--- /dev/null
+++ b/modules/popcount-tests
@@ -0,0 +1,10 @@
+Files:
+tests/test-popcount.c
+
+Depends-on:
+
+configure.ac:
+
+Makefile.am:
+TESTS += test-popcount
+check_PROGRAMS += test-popcount

new file mode 100644
--- /dev/null
+++ b/tests/test-popcount.c
@@ -0,0 +1,81 @@
+/*
+ * Copyright (C) 2007 Free Software Foundation
+ *
+ * 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 Ben Pfaff.  */
+
+#include <config.h>
+
+#include "popcount.h"
+
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#define ASSERT(expr)                                            \
+  do                                                            \
+    {                                                           \
+      if (!(expr))                                              \
+        {                                                       \
+          fprintf (stderr, "%s:%d: assertion \"%s\" failed\n",  \
+                   __FILE__, __LINE__, #expr);                  \
+          abort ();                                             \
+        }                                                       \
+    }                                                           \
+  while (0)
+
+#define UINT_BIT (sizeof (unsigned int) * CHAR_BIT)
+#define ULONG_BIT (sizeof (unsigned long int) * CHAR_BIT)
+#define ULLONG_BIT (sizeof (unsigned long long int) * CHAR_BIT)
+
+#ifndef ULLONG_MAX
+# define HALF (1ULL << (sizeof (unsigned long long int) * CHAR_BIT - 1))
+# define ULLONG_MAX (HALF - 1 + HALF)
+#endif
+
+int
+main (int argc, char *argv[])
+{
+  int i, j;
+
+#define TEST_POPCOUNT(FUNC, TYPE, BITS, MAX, ONE)       \
+  ASSERT (FUNC (0) == 0);                               \
+  for (i = 0; i < BITS; i++)                            \
+    {                                                   \
+      ASSERT (FUNC (ONE << i) == 1);                    \
+      for (j = i + 1; j < BITS; j++)                    \
+        ASSERT (FUNC ((ONE << i) | (ONE << j)) == 2);   \
+    }                                                   \
+  for (i = 0; i < 1000; i++)                            \
+    {                                                   \
+      TYPE value = rand () ^ (rand () << 31 << 1);      \
+      int count = 0;                                    \
+      for (j = 0; j < BITS; j++)                        \
+        count += (value & (ONE << j)) != 0;             \
+      ASSERT (count == FUNC (value));                   \
+    }                                                   \
+  ASSERT (FUNC (MAX) == BITS);
+
+  TEST_POPCOUNT (popcount, unsigned int, UINT_BIT, UINT_MAX, 1U);
+  TEST_POPCOUNT (popcountl, unsigned long int, ULONG_BIT, ULONG_MAX, 1UL);
+#ifdef HAVE_UNSIGNED_LONG_LONG_INT
+  TEST_POPCOUNT (popcountll,
+                 unsigned long long int, ULLONG_BIT, ULLONG_MAX, 1ULL);
+#endif
+
+  return 0;
+}