Fix bug in g_bit_nth_lsf (#371631) and use __builtin_clzl for

2007-01-03  Behdad Esfahbod  <behdad@gnome.org>

        * glib/gutils.h: Fix bug in g_bit_nth_lsf (#371631) and use 
        __builtin_clzl for g_bit_storage if available (#371670).

        * tests/Makefile.am:
        * tests/bit-test.c: New test, to test g_bit_* operations against
        naive and builtin implementations.


svn path=/trunk/; revision=5200

ChangeLog

@@ -1,3 +1,12 @@
+2007-01-03  Behdad Esfahbod  <behdad@gnome.org>
+
+	* glib/gutils.h: Fix bug in g_bit_nth_lsf (#371631) and use
+	__builtin_clzl for g_bit_storage if available (#371670).
+
+	* tests/Makefile.am:
+	* tests/bit-test.c: New test, to test g_bit_* operations against
+	naive and builtin implementations.
+
 2007-01-02  Behdad Esfahbod  <behdad@gnome.org>
 
 	* configure.in: Avoid more warnings from running libtool --config.

glib/gutils.h

@@ -250,10 +250,10 @@ gchar*  g_find_program_in_path  (const gchar *program);
 /* Bit tests
  */
 G_INLINE_FUNC gint	g_bit_nth_lsf (gulong  mask,
-				       gint    nth_bit);
+				       gint    nth_bit) G_GNUC_CONST;
 G_INLINE_FUNC gint	g_bit_nth_msf (gulong  mask,
-				       gint    nth_bit);
+				       gint    nth_bit) G_GNUC_CONST;
-G_INLINE_FUNC guint	g_bit_storage (gulong  number);
+G_INLINE_FUNC guint	g_bit_storage (gulong  number) G_GNUC_CONST;
 
 /* Trash Stacks
  * elements need to be >= sizeof (gpointer)
@@ -277,33 +277,36 @@ G_INLINE_FUNC gint
 g_bit_nth_lsf (gulong mask,
 	       gint   nth_bit)
 {
-  do
+  if (G_UNLIKELY (nth_bit < -1))
+    nth_bit = -1;
+  while (nth_bit < ((GLIB_SIZEOF_LONG * 8) - 1))
     {
       nth_bit++;
       if (mask & (1UL << nth_bit))
 	return nth_bit;
     }
-  while (nth_bit < ((GLIB_SIZEOF_LONG * 8) - 1));
   return -1;
 }
 G_INLINE_FUNC gint
 g_bit_nth_msf (gulong mask,
 	       gint   nth_bit)
 {
-  if (nth_bit < 0)
+  if (nth_bit < 0 || G_UNLIKELY (nth_bit > GLIB_SIZEOF_LONG * 8))
     nth_bit = GLIB_SIZEOF_LONG * 8;
-  do
+  while (nth_bit > 0)
     {
       nth_bit--;
       if (mask & (1UL << nth_bit))
 	return nth_bit;
     }
-  while (nth_bit > 0);
   return -1;
 }
 G_INLINE_FUNC guint
 g_bit_storage (gulong number)
 {
+#if defined(__GNUC__) && (__GNUC__ >= 4) && defined(__OPTIMIZE__)
+  return number ? GLIB_SIZEOF_LONG * 8 - __builtin_clzl(number) : 1;
+#else
   register guint n_bits = 0;
   
   do
@@ -313,6 +316,7 @@ g_bit_storage (gulong number)
     }
   while (number);
   return n_bits;
+#endif
 }
 G_INLINE_FUNC void
 g_trash_stack_push (GTrashStack **stack_p,

tests/Makefile.am

@@ -65,6 +65,7 @@ test_programs =					\
 	atomic-test				\
 	array-test				\
 	base64-test				\
+	bit-test				\
 	$(CXX_TEST)				\
 	child-test				\
 	completion-test				\
@@ -130,6 +131,7 @@ module_ldadd = $(libgmodule) $(G_MODULE_LIBS) $(progs_ldadd)
 atomic_test_LDADD = $(progs_ldadd)
 array_test_LDADD = $(progs_ldadd)
 base64_test_LDADD = $(progs_ldadd)
+bit_test_LDADD = $(progs_ldadd)
 bookmarkfile_test_LDADD = $(progs_ldadd)
 child_test_LDADD = $(thread_ldadd)
 completion_test_LDADD = $(progs_ldadd)

tests/bit-test.c

@@ -0,0 +1,145 @@
+#include <glib.h>
+
+#if defined(__GNUC__) && (__GNUC__ >= 4)
+# define TEST_BUILTINS 1
+#else
+# define TEST_BUILTINS 0
+#endif
+
+#if TEST_BUILTINS
+static gint
+builtin_bit_nth_lsf1 (gulong mask, gint nth_bit)
+{
+  if (nth_bit >= 0)
+    {
+      if (G_LIKELY (nth_bit < GLIB_SIZEOF_LONG * 8 - 1))
+	mask &= -(1<<(nth_bit+1));
+      else
+	mask = 0;
+    }
+  return __builtin_ffsl(mask) - 1;
+}
+
+static gint
+builtin_bit_nth_lsf2 (gulong mask, gint nth_bit)
+{
+  if (nth_bit >= 0)
+    {
+      if (G_LIKELY (nth_bit < GLIB_SIZEOF_LONG * 8 - 1))
+	mask &= -(1<<(nth_bit+1));
+      else
+	mask = 0;
+    }
+  return mask ? __builtin_ctzl(mask) : -1;
+}
+
+static gint
+builtin_bit_nth_msf (gulong mask, gint nth_bit)
+{
+  if (nth_bit >= 0 && nth_bit < GLIB_SIZEOF_LONG * 8)
+    mask &= (1<<nth_bit)-1;
+  return mask ? GLIB_SIZEOF_LONG * 8 - 1 - __builtin_clzl(mask) : -1;
+}
+
+
+static guint
+builtin_bit_storage (gulong number)
+{
+  return number ? GLIB_SIZEOF_LONG * 8 - __builtin_clzl(number) : 1;
+}
+#endif
+
+
+static gint
+naive_bit_nth_lsf (gulong mask, gint   nth_bit)
+{
+  if (G_UNLIKELY (nth_bit < -1))
+    nth_bit = -1;
+  while (nth_bit < ((GLIB_SIZEOF_LONG * 8) - 1))
+    {
+      nth_bit++;
+      if (mask & (1UL << nth_bit))
+	return nth_bit;
+    }
+  return -1;
+}
+
+static gint
+naive_bit_nth_msf (gulong mask, gint   nth_bit)
+{
+  if (nth_bit < 0 || G_UNLIKELY (nth_bit > GLIB_SIZEOF_LONG * 8))
+    nth_bit = GLIB_SIZEOF_LONG * 8;
+  while (nth_bit > 0)
+    {
+      nth_bit--;
+      if (mask & (1UL << nth_bit))
+	return nth_bit;
+    }
+  return -1;
+}
+
+static guint
+naive_bit_storage (gulong number)
+{
+  register guint n_bits = 0;
+  
+  do
+    {
+      n_bits++;
+      number >>= 1;
+    }
+  while (number);
+  return n_bits;
+}
+
+
+
+#define TEST(f1, f2, i) \
+	if (f1 (i) != f2 (i)) { \
+		g_error (G_STRINGIFY (f1) " (%lu) = %d; " \
+			 G_STRINGIFY (f2) " (%lu) = %d; ", \
+			 i, f1 (i), \
+			 i, f2 (i)); \
+		return 1; \
+	}
+#define TEST2(f1, f2, i, n) \
+	if (f1 (i, n) != f2 (i, n)) { \
+		g_error (G_STRINGIFY (f1) " (%lu, %d) = %d; " \
+			 G_STRINGIFY (f2) " (%lu, %d) = %d; ", \
+			 i, n, f1 (i, n), \
+			 i, n, f2 (i, n)); \
+		return 1; \
+	}
+
+int
+main (void)
+{
+  gulong i;
+  gint nth_bit;
+
+  /* we loop like this: 0, -1, 1, -2, 2, -3, 3, ... */
+  for (i = 0; (glong)i < 1500 ; i = -(i+((glong)i>=0))) {
+
+#if TEST_BUILTINS
+    TEST (naive_bit_storage, builtin_bit_storage, i);
+#endif
+    TEST (naive_bit_storage, g_bit_storage, i);
+
+    for (nth_bit = -3; nth_bit <= 2 + GLIB_SIZEOF_LONG * 8; nth_bit++) {
+
+#if TEST_BUILTINS
+      TEST2 (naive_bit_nth_lsf, builtin_bit_nth_lsf1, i, nth_bit);
+      TEST2 (naive_bit_nth_lsf, builtin_bit_nth_lsf2, i, nth_bit);
+#endif
+      TEST2 (naive_bit_nth_lsf, g_bit_nth_lsf, i, nth_bit);
+
+#if TEST_BUILTINS
+      TEST2 (naive_bit_nth_msf, builtin_bit_nth_msf, i, nth_bit);
+#endif
+      TEST2 (naive_bit_nth_msf, g_bit_nth_msf, i, nth_bit);
+
+    }
+  }
+
+  return 0;
+}