BleuStats.cpp

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//Copyright (c) 2012, University of Cambridge
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#include "BleuStats.h"
#include <cmath>
#include <cstddef>
using std::min;
using std::log;

const unsigned int BleuStats::MAX_BLEU_ORDER = 4;

BleuStats::BleuStats() : refLength (0) {
  tots.resize (MAX_BLEU_ORDER, 0);
  hits.resize (MAX_BLEU_ORDER, 0);
}

BleuStats::Error BleuStats::ComputeError (const unsigned int order) const {
  double logBleu = 0.0;
  double logBrev = 0.0;
  for (unsigned int n = 0; n < order; ++n) {
    logBleu += log ( (double) this->hits[n] / (double) this->tots[n]);
  }
  logBleu *= 1 / (double) BleuStats::MAX_BLEU_ORDER;
  logBrev = min (0.0, 1 - this->refLength / (double) (this->tots[0]) );
  return Error (exp (logBleu + logBrev), exp (logBrev) );
}

ostream& operator<< (ostream& o, const BleuStats& b) {
  for (unsigned int n = 0; n < BleuStats::MAX_BLEU_ORDER; ++n) {
    if (n > 0) {
      o << "\t";
    }
    o << b.hits[n] << "\t" << b.tots[n];
  }
  o << "\t" << b.refLength;
  return o;
}

BleuStats operator+ (const BleuStats& bs1, const BleuStats& bs2) {
  BleuStats bs;
  for (unsigned int n = 0; n < BleuStats::MAX_BLEU_ORDER; ++n) {
    bs.hits[n] = bs1.hits[n] + bs2.hits[n];
    bs.tots[n] = bs1.tots[n] + bs2.tots[n];
  }
  bs.refLength = bs1.refLength + bs2.refLength;
  return bs;
}

BleuStats operator- (const BleuStats& bs1, const BleuStats& bs2) {
  BleuStats bs;
  bs.refLength = bs1.refLength - bs2.refLength;
  for (unsigned int n = 0; n < BleuStats::MAX_BLEU_ORDER; ++n) {
    bs.tots[n] = bs1.tots[n] - bs2.tots[n];
    bs.hits[n] = bs1.hits[n] - bs2.hits[n];
  }
  return bs;
}

ostream& operator<< (ostream& o, const Bleu& b) {
  o << b.m_bleu << " " << b.m_brev;
  return o;
}

bool operator> (Bleu& b1, Bleu& b2) {
  return b1.m_bleu > b2.m_bleu;
}