341 lines
16 KiB
C
341 lines
16 KiB
C
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// fstext/context-fst.h
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// Copyright 2009-2011 Microsoft Corporation
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// 2018 Johns Hopkins University (author: Daniel Povey)
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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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//
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// This file includes material from the OpenFST Library v1.2.7 available at
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// http://www.openfst.org and released under the Apache License Version 2.0.
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//
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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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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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// Copyright 2005-2010 Google, Inc.
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// Author: riley@google.com (Michael Riley)
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#ifndef KALDI_FSTEXT_CONTEXT_FST_H_
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#define KALDI_FSTEXT_CONTEXT_FST_H_
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/* This header defines a context FST "C" (the "C" in "HCLG") which transduces
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from symbols representing phone context windows (e.g. "a, b, c") to
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individual phones, e.g. "a". Search for "hbka.pdf" ("Speech Recognition
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with Weighted Finite State Transducers") by M. Mohri, for more context.
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*/
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#include <unordered_map>
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using std::unordered_map;
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#include <algorithm>
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#include <string>
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#include <vector>
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#include <fst/fstlib.h>
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#include <fst/fst-decl.h>
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#include "util/const-integer-set.h"
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#include "fstext/deterministic-fst.h"
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namespace fst {
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/// Utility function for writing ilabel-info vectors to disk.
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void WriteILabelInfo(std::ostream &os, bool binary,
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const std::vector<std::vector<int32> > &ilabel_info);
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/// Utility function for reading ilabel-info vectors from disk.
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void ReadILabelInfo(std::istream &is, bool binary,
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std::vector<std::vector<int32> > *ilabel_info);
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/// The following function is mainly of use for printing and debugging.
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SymbolTable *CreateILabelInfoSymbolTable(const std::vector<std::vector<int32> > &ilabel_info,
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const SymbolTable &phones_symtab,
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std::string separator,
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std::string disambig_prefix); // e.g. separator = "/", disambig_prefix = "#"
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/**
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Used in the command-line tool fstcomposecontext. It creates a context FST and
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composes it on the left with "ifst" to make "ofst". It outputs the label
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information to ilabels_out. "ifst" is mutable because we need to add the
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subsequential loop.
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@param [in] disambig_syms List of disambiguation symbols, e.g. the integer
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ids of #0, #1, #2 ... in the phones.txt.
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@param [in] context_width Size of context window, e.g. 3 for triphone.
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@param [in] central_position Central position in phonetic context window
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(zero-based index), e.g. 1 for triphone.
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@param [in,out] ifst The FST we are composing with C (e.g. LG.fst), mustable because
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we need to add the subsequential loop to it.
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@param [out] ofst Composed output FST (would be CLG.fst).
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@param [out] ilabels_out Vector, indexed by ilabel of CLG.fst, providing information
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about the meaning of that ilabel; see
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"http://kaldi-asr.org/doc/tree_externals.html#tree_ilabel".
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@param [in] project_ifst This is intended only to be set to true
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in the program 'fstmakecontextfst'... if true, it will
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project on the input after adding the subsequential loop
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to 'ifst', which allows us to reconstruct the context
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fst C.fst.
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*/
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void ComposeContext(const std::vector<int32> &disambig_syms,
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int32 context_width, int32 central_position,
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VectorFst<StdArc> *ifst,
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VectorFst<StdArc> *ofst,
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std::vector<std::vector<int32> > *ilabels_out,
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bool project_ifst = false);
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/**
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Modifies an FST so that it transuces the same paths, but the input side of the
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paths can all have the subsequential symbol '$' appended to them any number of
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times (we could easily specify the number of times, but accepting any number of
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repetitions is just more convenient). The actual way we do this is for each
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final state, we add a transition with weight equal to the final-weight of that
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state, with input-symbol '$' and output-symbols \<eps\>, and ending in a new
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super-final state that has unit final-probability and a unit-weight self-loop
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with '$' on its input and \<eps\> on its output. The reason we don't just
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add a loop to each final-state has to do with preserving stochasticity
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(see \ref fst_algo_stochastic). We keep the final-probability in all the
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original final-states rather than setting them to zero, so the resulting FST
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can accept zero '$' symbols at the end (in case we had no right context).
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*/
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void AddSubsequentialLoop(StdArc::Label subseq_symbol,
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MutableFst<StdArc> *fst);
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/*
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InverseContextFst represents the inverse of the context FST "C" (the "C" in
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"HCLG") which transduces from symbols representing phone context windows
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(e.g. "a, b, c") to individual phones, e.g. "a". So InverseContextFst
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transduces from phones to symbols representing phone context windows. The
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point is that the inverse is deterministic, so the DeterministicOnDemandFst
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interface is applicable, which turns out to be a convenient way to implement
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this.
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This doesn't implement the full Fst interface, it implements the
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DeterministicOnDemandFst interface which is much simpler and which is
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sufficient for what we need to do with this.
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Search for "hbka.pdf" ("Speech Recognition with Weighted Finite State
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Transducers") by M. Mohri, for more context.
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*/
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class InverseContextFst: public DeterministicOnDemandFst<StdArc> {
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public:
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typedef StdArc Arc;
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typedef typename StdArc::StateId StateId;
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typedef typename StdArc::Weight Weight;
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typedef typename StdArc::Label Label;
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/**
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Constructor.
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@param [in] subsequential_symbol The integer id of the 'subsequential symbol'
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(usually represented as '$') that terminates sequences on the
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output of C.fst (input of InverseContextFst). Search for
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"quential" in https://cs.nyu.edu/~mohri/pub/hbka.pdf.
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This may just be the first unused integer id. Must be nonzer.
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@param [in] phones List of integer ids of phones, as you would see in phones.txt
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@param [in] disambig_syms List of integer ids of disambiguation symbols,
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e.g. the ids of #0, #1, #2 in phones.txt
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@param [in] context_width Size of context window, e.g. 3 for triphone.
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@param [in] central_position Central position in context window (zero-based),
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e.g. 1 for triphone.
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See \ref graph_context for more details.
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*/
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InverseContextFst(Label subsequential_symbol,
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const std::vector<int32>& phones,
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const std::vector<int32>& disambig_syms,
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int32 context_width,
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int32 central_position);
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virtual StateId Start() { return 0; }
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virtual Weight Final(StateId s);
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/// Note: ilabel must not be epsilon.
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virtual bool GetArc(StateId s, Label ilabel, Arc *arc);
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~InverseContextFst() { }
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// Returns a reference to a vector<vector<int32> > with information about all
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// the input symbols of C (i.e. all the output symbols of this
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// InverseContextFst). See
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// "http://kaldi-asr.org/doc/tree_externals.html#tree_ilabel".
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const std::vector<std::vector<int32> > &IlabelInfo() const {
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return ilabel_info_;
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}
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// A way to destructively obtain the ilabel-info. Only do this if you
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// are just about to destroy this object.
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void SwapIlabelInfo(std::vector<std::vector<int32> > *vec) { ilabel_info_.swap(*vec); }
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private:
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/// Returns the state-id corresponding to this vector of phones; creates the
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/// state it if necessary. Requires seq.size() == context_width_ - 1.
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StateId FindState(const std::vector<int32> &seq);
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/// Finds the label index corresponding to this context-window of phones
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/// (likely of width context_width_). Inserts it into the
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/// ilabel_info_/ilabel_map_ tables if necessary.
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Label FindLabel(const std::vector<int32> &label_info);
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inline bool IsDisambigSymbol(Label lab) { return (disambig_syms_.count(lab) != 0); }
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inline bool IsPhoneSymbol(Label lab) { return (phone_syms_.count(lab) != 0); }
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/// Create disambiguation-symbol self-loop arc; where 'ilabel' must correspond to
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/// a disambiguation symbol. Called from CreateArc().
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inline void CreateDisambigArc(StateId s, Label ilabel, Arc *arc);
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/// Creates an arc, this function is to be called only when 'ilabel'
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/// corresponds to a phone. Called from CreateArc(). The olabel may end be
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/// epsilon, instead of a phone-in-context, if the system has right context
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/// and we are very near the beginning of the phone sequence.
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inline void CreatePhoneOrEpsArc(StateId src, StateId dst, Label ilabel,
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const std::vector<int32> &phone_seq, Arc *arc);
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/// If phone_seq is nonempty then this function it left by one and appends
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/// 'label' to it, otherwise it does nothing. We expect (but do not check)
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/// that phone_seq->size() == context_width_ - 1.
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inline void ShiftSequenceLeft(Label label, std::vector<int32> *phone_seq);
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/// This utility function does something equivalent to the following 3 steps:
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/// *full_phone_sequence = seq;
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/// full_phone_sequence->append(label)
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/// Replace any values equal to 'subsequential_symbol_' in
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/// full_phone_sequence with zero (this is to avoid having to keep track of
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/// the value of 'subsequential_symbol_' outside of this program).
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/// This function assumes that seq.size() == context_width_ - 1, and also that
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/// 'subsequential_symbol_' does not appear in positions 0 through
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/// central_position_ of 'seq'.
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inline void GetFullPhoneSequence(const std::vector<int32> &seq, Label label,
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std::vector<int32> *full_phone_sequence);
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// Map type to map from vectors of int32 (representing phonetic contexts,
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// which will be of dimension context_width - 1) to StateId (corresponding to
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// the state index in this FST).
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typedef unordered_map<std::vector<int32>, StateId,
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kaldi::VectorHasher<int32> > VectorToStateMap;
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// Map type to map from vectors of int32 (representing ilabel-info,
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// see http://kaldi-asr.org/doc/tree_externals.html#tree_ilabel) to
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// Label (the output label in this FST).
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typedef unordered_map<std::vector<int32>, Label,
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kaldi::VectorHasher<int32> > VectorToLabelMap;
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// Sometimes called N, context_width_ this is the width of the
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// phonetic context, e.g. 3 for triphone, 2 for biphone, one for monophone.
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// It is a user-specified value.
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int32 context_width_;
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// Sometimes called P, central_position_ is is the (zero-based) "central
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// position" in the context window, meaning the phone that is "in" a certain
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// context. The most widely used values of (context-width, central-position)
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// are: (3,1) for triphone, (1,0) for monophone, and (2, 1) for left biphone.
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// This is also specified by the user. As an example, in the left-biphone
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// [ 5, 6 ], we view it as "the phone numbered 6 with the phone numbered 5 as
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// its left-context".
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int32 central_position_;
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// The following three variables were also passed in by the caller:
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// 'phone_syms_' are a set of phone-ids, typically 1, 2, .. num_phones.
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kaldi::ConstIntegerSet<Label> phone_syms_;
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// disambig_syms_ is the set of integer ids of the disambiguation symbols,
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// usually represented in text form as #0, #1, #2, etc. These are inserted
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// into the grammar (for #0) and the lexicon (for #1, #2, ...) in order to
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// make the composed FSTs determinizable. They are treated "specially" by the
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// context FST in that they are not part of the context, they are just "passed
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// through" via self-loops. See the Mohri chapter mrentioned above for more
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// information.
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kaldi::ConstIntegerSet<Label> disambig_syms_;
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// subsequential_symbol_, represented as "$" in the Mohri chapter mentioned
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// above, is something which terminates phonetic sequences to force out the
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// last phones-in-context. In our implementation it's added to det(LG) as a
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// self-loop on final states before composing with C.
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// (c.f. AddSubsequentialLoop()).
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Label subsequential_symbol_;
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// pseudo_eps_symbol_, which in printed form we refer to as "#-1", is a symbol that
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// appears on the ilabels of the context transducer C, i.e. the olabels of this
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// FST which is C's inverse. It is a symbol we introduce to solve a special problem
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// in systems with right-context (context_width_ > central_position_ + 1) that
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// use disambiguation symbols. It exists to prevent CLG from being nondeterminizable.
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//
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// The issue is that, in this case, the disambiguation symbols are shifted
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// left w.r.t. the phones, and there becomes an ambiguity, if a disambiguation
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// symbol appears at the start of a sequence on the input of CLG, about
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// whether it was at the very start of the input of LG, or just after, say,
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// the first real phone. This can lead to determinization failure under
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// certain circumstances. What we do if we need pseudo_eps_symbol_ to be not
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// epsilon, we create a special symbol with symbol-id 1 and sequence
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// representation (ilabels entry) [ 0 ] .
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int32 pseudo_eps_symbol_;
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// maps from vector<int32>, representing phonetic contexts of length
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// context_width_ - 1, to StateId. (The states of the "C" fst correspond to
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// phonetic contexts, but we only create them as and when they are needed).
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VectorToStateMap state_map_;
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// The inverse of 'state_map_': gives us the phonetic context corresponding to
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// each state-id.
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std::vector<std::vector<int32> > state_seqs_;
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// maps from vector<int32>, representing phonetic contexts of length
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// context_width_ - 1, to Label. These are actually the output labels of this
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// InverseContextFst (because of the "Inverse" part), but for historical
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// reasons and because we've used the term ilabels" in the documentation, we
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// still call these "ilabels").
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VectorToLabelMap ilabel_map_;
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// ilabel_info_ is the reverse map of ilabel_map_.
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// Indexed by olabel (although we call this ilabel_info_ for historical
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// reasons and because is for the ilabels of C), ilabel_info_[i] gives
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// information about the meaning of each symbol on the input of C
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// aka the output of inv(C).
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// See "http://kaldi-asr.org/doc/tree_externals.html#tree_ilabel".
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std::vector<std::vector<int32> > ilabel_info_;
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};
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} // namespace fst
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#endif // KALDI_FSTEXT_CONTEXT_FST_H_
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