Moved bits.h from O3D to Chrome base.

base/bits.h

+// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// This file defines some bit utilities.
+
+#ifndef BASE_BITS_H_
+#define BASE_BITS_H_
+
+#include "base/basictypes.h"
+#include "base/logging.h"
+
+namespace base {
+namespace bits {
+
+// Returns the integer i such as 2^i <= n < 2^(i+1)
+inline int Log2Floor(uint32 n) {
+  if (n == 0)
+    return -1;
+  int log = 0;
+  uint32 value = n;
+  for (int i = 4; i >= 0; --i) {
+    int shift = (1 << i);
+    uint32 x = value >> shift;
+    if (x != 0) {
+      value = x;
+      log += shift;
+    }
+  }
+  DCHECK_EQ(value, 1u);
+  return log;
+}
+
+// Returns the integer i such as 2^(i-1) < n <= 2^i
+inline int Log2Ceiling(uint32 n) {
+  if (n == 0) {
+    return -1;
+  } else {
+    // Log2Floor returns -1 for 0, so the following works correctly for n=1.
+    return 1 + Log2Floor(n - 1);
+  }
+}
+
+}  // namespace bits
+}  // namespace base
+
+#endif  // BASE_BITS_H_