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117 lines
5.0 KiB
117 lines
5.0 KiB
// fstext/determinize-star.h
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// Copyright 2009-2011 Microsoft Corporation
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// 2014 Guoguo Chen
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// 2015 Hainan Xu
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// See ../../COPYING for clarification regarding multiple authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// THIS CODE IS PROVIDED *AS IS* BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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// KIND, EITHER EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION ANY IMPLIED
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// WARRANTIES OR CONDITIONS OF TITLE, FITNESS FOR A PARTICULAR PURPOSE,
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// MERCHANTABLITY OR NON-INFRINGEMENT.
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// See the Apache 2 License for the specific language governing permissions and
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// limitations under the License.
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#ifndef KALDI_FSTEXT_DETERMINIZE_STAR_H_
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#define KALDI_FSTEXT_DETERMINIZE_STAR_H_
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#include <fst/fst-decl.h>
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#include <fst/fstlib.h>
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#include <algorithm>
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#include <map>
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#include <set>
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#include <stdexcept> // this algorithm uses exceptions
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#include <vector>
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namespace fst {
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/// \addtogroup fst_extensions
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/// @{
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// For example of usage, see test-determinize-star.cc
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/*
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DeterminizeStar implements determinization with epsilon removal, which we
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distinguish with a star.
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We define a determinized* FST as one in which no state has more than one
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transition with the same input-label. Epsilon input labels are not allowed
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except starting from states that have exactly one arc exiting them (and are
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not final). [In the normal definition of determinized, epsilon-input labels
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are not allowed at all, whereas in Mohri's definition, epsilons are treated
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as ordinary symbols]. The determinized* definition is intended to simulate
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the effect of allowing strings of output symbols at each state.
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The algorithm implemented here takes an Fst<Arc>, and a pointer to a
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MutableFst<Arc> where it puts its output. The weight type is assumed to be a
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float-weight. It does epsilon removal and determinization.
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This algorithm may fail if the input has epsilon cycles under
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certain circumstances (i.e. the semiring is non-idempotent, e.g. the log
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semiring, or there are negative cost epsilon cycles).
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This implementation is much less fancy than the one in fst/determinize.h, and
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does not have an "on-demand" version.
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The algorithm is a fairly normal determinization algorithm. We keep in
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memory the subsets of states, together with their leftover strings and their
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weights. The only difference is we detect input epsilon transitions and
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treat them "specially".
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*/
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// This algorithm will be slightly faster if you sort the input fst on input
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// label.
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/**
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This function implements the normal version of DeterminizeStar, in which the
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output strings are represented using sequences of arcs, where all but the
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first one has an epsilon on the input side. The debug_ptr argument is an
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optional pointer to a bool that, if it becomes true while the algorithm is
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executing, the algorithm will print a traceback and terminate (used in
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fstdeterminizestar.cc debug non-terminating determinization).
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If max_states is positive, it will stop determinization and throw an
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exception as soon as the max-states is reached. This can be useful in test.
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If allow_partial is true, the algorithm will output partial results when the
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specified max_states is reached (when larger than zero), instead of throwing
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out an error.
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Caution, the return status is un-intuitive: this function will return false
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if determinization completed normally, and true if it was stopped early by
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reaching the 'max-states' limit, and a partial FST was generated.
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*/
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template <class F>
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bool DeterminizeStar(F &ifst, MutableFst<typename F::Arc> *ofst, // NOLINT
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float delta = kDelta, bool *debug_ptr = NULL,
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int max_states = -1, bool allow_partial = false);
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/* This is a version of DeterminizeStar with a slightly more "natural" output
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format, where the output sequences are encoded using the GallicArc (i.e. the
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output symbols are strings. If max_states is positive, it will stop
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determinization and throw an exception as soon as the max-states is reached.
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This can be useful in test. If allow_partial is true, the algorithm will
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output partial results when the specified max_states is reached (when larger
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than zero), instead of throwing out an error.
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Caution, the return status is un-intuitive: this function will return false
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if determinization completed normally, and true if it was stopped early by
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reaching the 'max-states' limit, and a partial FST was generated.
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*/
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template <class F>
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bool DeterminizeStar(F &ifst, // NOLINT
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MutableFst<GallicArc<typename F::Arc> > *ofst,
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float delta = kDelta, bool *debug_ptr = NULL,
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int max_states = -1, bool allow_partial = false);
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/// @} end "addtogroup fst_extensions"
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} // end namespace fst
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#include "fstext/determinize-star-inl.h"
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#endif // KALDI_FSTEXT_DETERMINIZE_STAR_H_
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