1// push.h 2// 3// Licensed under the Apache License, Version 2.0 (the "License"); 4// you may not use this file except in compliance with the License. 5// You may obtain a copy of the License at 6// 7// http://www.apache.org/licenses/LICENSE-2.0 8// 9// Unless required by applicable law or agreed to in writing, software 10// distributed under the License is distributed on an "AS IS" BASIS, 11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12// See the License for the specific language governing permissions and 13// limitations under the License. 14// 15// Author: allauzen@cs.nyu.edu (Cyril Allauzen) 16// 17// \file 18// Class to reweight/push an FST. 19 20#ifndef FST_LIB_PUSH_H__ 21#define FST_LIB_PUSH_H__ 22 23#include "fst/lib/factor-weight.h" 24#include "fst/lib/fst.h" 25#include "fst/lib/map.h" 26#include "fst/lib/reweight.h" 27#include "fst/lib/shortest-distance.h" 28 29namespace fst { 30 31// Pushes the weights in FST in the direction defined by TYPE. If 32// pushing towards the initial state, the sum of the weight of the 33// outgoing transitions and final weight at a non-initial state is 34// equal to One() in the resulting machine. If pushing towards the 35// final state, the same property holds on the reverse machine. 36// 37// Weight needs to be left distributive when pushing towards the 38// initial state and right distributive when pushing towards the final 39// states. 40template <class Arc> 41void Push(MutableFst<Arc> *fst, ReweightType type) { 42 vector<typename Arc::Weight> distance; 43 ShortestDistance(*fst, &distance, type == REWEIGHT_TO_INITIAL); 44 Reweight(fst, distance, type); 45} 46 47 48const uint32 kPushWeights = 0x0001; 49const uint32 kPushLabels = 0x0002; 50 51// OFST obtained from IFST by pushing weights and/or labels according 52// to PTYPE in the direction defined by RTYPE. Weight needs to be 53// left distributive when pushing weights towards the initial state 54// and right distributive when pushing weights towards the final 55// states. 56template <class Arc, ReweightType rtype> 57void Push(const Fst<Arc> &ifst, MutableFst<Arc> *ofst, uint32 ptype) { 58 59 if (ptype == kPushWeights) { 60 *ofst = ifst; 61 Push(ofst, rtype); 62 } else if (ptype & kPushLabels) { 63 const StringType stype = rtype == REWEIGHT_TO_INITIAL 64 ? STRING_LEFT 65 : STRING_RIGHT; 66 vector<typename GallicArc<Arc, stype>::Weight> gdistance; 67 VectorFst< GallicArc<Arc, stype> > gfst; 68 Map(ifst, &gfst, ToGallicMapper<Arc, stype>()); 69 if (ptype == (kPushWeights | kPushLabels)) { 70 ShortestDistance(gfst, &gdistance, rtype == REWEIGHT_TO_INITIAL); 71 } else { 72 MapFst<Arc, Arc, RmWeightMapper<Arc> > 73 uwfst(ifst, RmWeightMapper<Arc>()); 74 MapFst<Arc, GallicArc<Arc, stype>, ToGallicMapper<Arc, stype> > 75 guwfst(uwfst, ToGallicMapper<Arc, stype>()); 76 ShortestDistance(guwfst, &gdistance, rtype == REWEIGHT_TO_INITIAL); 77 } 78 Reweight(&gfst, gdistance, rtype); 79 FactorWeightFst< GallicArc<Arc, stype>, GallicFactor<typename Arc::Label, 80 typename Arc::Weight, stype> > fwfst(gfst); 81 Map(fwfst, ofst, FromGallicMapper<Arc, stype>()); 82 } else { 83 *ofst = ifst; 84 } 85} 86 87} // namespace fst 88 89#endif /* FST_LIB_PUSH_H_ */ 90