| |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| // |
| // Copyright 2005-2010 Google, Inc. |
| // Author: sorenj@google.com (Jeffrey Sorensen) |
| // dr@google.com (Doug Rohde) |
| |
| #ifndef FST_EXTENSIONS_NGRAM_NTHBIT_H_ |
| #define FST_EXTENSIONS_NGRAM_NTHBIT_H_ |
| |
| #include <fst/types.h> |
| |
| extern uint32 nth_bit_bit_offset[]; |
| |
| inline uint32 nth_bit(uint64 v, uint32 r) { |
| uint32 shift = 0; |
| uint32 c = __builtin_popcount(v & 0xffffffff); |
| uint32 mask = -(r > c); |
| r -= c & mask; |
| shift += (32 & mask); |
| |
| c = __builtin_popcount((v >> shift) & 0xffff); |
| mask = -(r > c); |
| r -= c & mask; |
| shift += (16 & mask); |
| |
| c = __builtin_popcount((v >> shift) & 0xff); |
| mask = -(r > c); |
| r -= c & mask; |
| shift += (8 & mask); |
| |
| return shift + ((nth_bit_bit_offset[(v >> shift) & 0xff] >> |
| ((r - 1) << 2)) & 0xf); |
| } |
| |
| #endif // FST_EXTENSIONS_NGRAM_NTHBIT_H_ |
