1// Copyright 2013 Google Inc. All Rights Reserved.
2//
3// Licensed under the Apache License, Version 2.0 (the "License");
4// you may not use this file except in compliance with the License.
5// You may obtain a copy of the License at
6//
7// http://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS,
11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12// See the License for the specific language governing permissions and
13// limitations under the License.
14//
15// Helper function for bit twiddling
16
17#ifndef WOFF2_PORT_H_
18#define WOFF2_PORT_H_
19
20namespace woff2 {
21
22typedef unsigned int       uint32;
23
24inline int Log2Floor(uint32 n) {
25#if defined(__GNUC__)
26  return n == 0 ? -1 : 31 ^ __builtin_clz(n);
27#else
28  if (n == 0)
29    return -1;
30  int log = 0;
31  uint32 value = n;
32  for (int i = 4; i >= 0; --i) {
33    int shift = (1 << i);
34    uint32 x = value >> shift;
35    if (x != 0) {
36      value = x;
37      log += shift;
38    }
39  }
40  assert(value == 1);
41  return log;
42#endif
43}
44
45} // namespace woff2
46#endif  // WOFF2_PORT_H_
47