/usr/include/fst/extensions/ngram/nthbit.h is in libfst-dev 1.6.3-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 | // See www.openfst.org for extensive documentation on this weighted
// finite-state transducer library.
#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_
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