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 20 namespace woff2 { 21 22 typedef unsigned int uint32; 23 Log2Floor(uint32 n)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