float DistortionScoreProducer::CalculateDistortionScore(const Hypothesis& hypo,
const WordsRange &prev, const WordsRange &curr, const int FirstGap) const
{
if(!StaticData::Instance().UseEarlyDistortionCost()) {
return - (float) hypo.GetInput().ComputeDistortionDistance(prev, curr);
}
else {
/* Pay distortion score as soon as possible, from Moore and Quirk MT Summit 2007
Definitions:
S : current source range
S' : last translated source phrase range
S'' : longest fully-translated initial segment
*/
int prefixEndPos = (int)FirstGap-1;
if((int)FirstGap==-1)
prefixEndPos = -1;
// case1: S is adjacent to S'' => return 0
if ((int) curr.GetStartPos() == prefixEndPos+1) {
IFVERBOSE(4) std::cerr<< "MQ07disto:case1" << std::endl;
return 0;
}
// case2: S is to the left of S' => return 2(length(S))
if ((int) curr.GetEndPos() < (int) prev.GetEndPos()) {
IFVERBOSE(4) std::cerr<< "MQ07disto:case2" << std::endl;
return (float) -2*(int)curr.GetNumWordsCovered();
}
// case3: S' is a subsequence of S'' => return 2(nbWordBetween(S,S'')+length(S))
if ((int) prev.GetEndPos() <= prefixEndPos) {
IFVERBOSE(4) std::cerr<< "MQ07disto:case3" << std::endl;
int z = (int)curr.GetStartPos()-prefixEndPos - 1;
return (float) -2*(z + (int)curr.GetNumWordsCovered());
}
// case4: otherwise => return 2(nbWordBetween(S,S')+length(S))
IFVERBOSE(4) std::cerr<< "MQ07disto:case4" << std::endl;
return (float) -2*((int)curr.GetNumWordsBetween(prev) + (int)curr.GetNumWordsCovered());
}
}
