mirror of
https://github.com/moses-smt/mosesdecoder.git
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44 lines
1.4 KiB
C++
44 lines
1.4 KiB
C++
#ifndef LM_BLANK_H
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#define LM_BLANK_H
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#include <limits>
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#include <stdint.h>
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#include <math.h>
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namespace lm {
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namespace ngram {
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/* Suppose "foo bar" appears with zero backoff but there is no trigram
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* beginning with these words. Then, when scoring "foo bar", the model could
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* return out_state containing "bar" or even null context if "bar" also has no
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* backoff and is never followed by another word. Then the backoff is set to
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* kNoExtensionBackoff. If the n-gram might be extended, then out_state must
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* contain the full n-gram, in which case kExtensionBackoff is set. In any
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* case, if an n-gram has non-zero backoff, the full state is returned so
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* backoff can be properly charged.
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* These differ only in sign bit because the backoff is in fact zero in either
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* case.
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*/
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const float kNoExtensionBackoff = -0.0;
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const float kExtensionBackoff = 0.0;
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const uint64_t kNoExtensionQuant = 0;
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const uint64_t kExtensionQuant = 1;
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inline void SetExtension(float &backoff) {
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if (backoff == kNoExtensionBackoff) backoff = kExtensionBackoff;
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}
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// This compiles down nicely.
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inline bool HasExtension(const float &backoff) {
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typedef union { float f; uint32_t i; } UnionValue;
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UnionValue compare, interpret;
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compare.f = kNoExtensionBackoff;
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interpret.f = backoff;
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return compare.i != interpret.i;
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}
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} // namespace ngram
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} // namespace lm
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#endif // LM_BLANK_H
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