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#ifndef LM_FILTER_WRAPPER_H
#define LM_FILTER_WRAPPER_H
#include "util/string_piece.hh"
#include <algorithm>
#include <string>
#include <vector>
namespace lm {
// Provide a single-output filter with the same interface as a
// multiple-output filter so clients code against one interface.
template <class Binary> class BinaryFilter {
public:
// Binary modes are just references (and a set) and it makes the API cleaner to copy them.
explicit BinaryFilter(Binary binary) : binary_(binary) {}
template <class Iterator, class Output> void AddNGram(const Iterator &begin, const Iterator &end, const StringPiece &line, Output &output) {
if (binary_.PassNGram(begin, end))
output.AddNGram(line);
}
template <class Output> void AddNGram(const StringPiece &ngram, const StringPiece &line, Output &output) {
AddNGram(util::TokenIter<util::SingleCharacter, true>(ngram, ' '), util::TokenIter<util::SingleCharacter, true>::end(), line, output);
}
void Flush() const {}
private:
Binary binary_;
};
// Wrap another filter to pay attention only to context words
template <class FilterT> class ContextFilter {
public:
typedef FilterT Filter;
explicit ContextFilter(Filter &backend) : backend_(backend) {}
template <class Output> void AddNGram(const StringPiece &ngram, const StringPiece &line, Output &output) {
// Find beginning of string or last space.
const char *last_space;
for (last_space = ngram.data() + ngram.size() - 1; last_space > ngram.data() && *last_space != ' '; --last_space) {}
backend_.AddNGram(StringPiece(ngram.data(), last_space - ngram.data()), line, output);
}
void Flush() const {}
private:
Filter backend_;
};
} // namespace lm
#endif // LM_FILTER_WRAPPER_H
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