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-rw-r--r--mteval/ns_cer.cc55
1 files changed, 55 insertions, 0 deletions
diff --git a/mteval/ns_cer.cc b/mteval/ns_cer.cc
new file mode 100644
index 00000000..a843d471
--- /dev/null
+++ b/mteval/ns_cer.cc
@@ -0,0 +1,55 @@
+#include "ns_cer.h"
+#include "tdict.h"
+
+static const unsigned kNUMFIELDS = 2;
+static const unsigned kEDITDISTANCE = 0;
+static const unsigned kCHARCOUNT = 1;
+
+bool CERMetric::IsErrorMetric() const {
+ return true;
+}
+
+unsigned CERMetric::SufficientStatisticsVectorSize() const {
+ return 2;
+}
+
+unsigned CERMetric::EditDistance(const std::string& hyp,
+ const std::string& ref) const {
+ const unsigned m = hyp.size(), n = ref.size();
+ std::vector<unsigned> edit((m + 1) * 2);
+ for(unsigned i = 0; i < n + 1; i++) {
+ for(unsigned j = 0; j < m + 1; j++) {
+ if(i == 0)
+ edit[j] = j;
+ else if(j == 0)
+ edit[(i%2)*(m+1)] = i;
+ else
+ edit[(i%2)*(m+1) + j] = std::min(std::min(edit[(i%2)*(m+1) + j-1] + 1,
+ edit[((i-1)%2)*(m+1) + j] + 1),
+ edit[((i-1)%2)*(m+1) + (j-1)]
+ + (hyp[j-1] == ref[i-1] ? 0 : 1));
+
+ }
+ }
+ return edit[(n%2)*(m+1) + m];
+}
+
+void CERMetric::ComputeSufficientStatistics(const std::vector<WordID>& hyp,
+ const std::vector<std::vector<WordID> >& refs,
+ SufficientStats* out) const {
+ out->fields.resize(kNUMFIELDS);
+ std::string hyp_str(TD::GetString(hyp));
+ float best_score = hyp_str.size();
+ for (size_t i = 0; i < refs.size(); ++i) {
+ std::string ref_str(TD::GetString(refs[i]));
+ float score = EditDistance(hyp_str, ref_str);
+ if (score < best_score) {
+ out->fields[kEDITDISTANCE] = score;
+ out->fields[kCHARCOUNT] = ref_str.size();
+ best_score = score;
+ }
+ }
+}
+float CERMetric::ComputeScore(const SufficientStats& stats) const {
+ return stats.fields[kEDITDISTANCE] / stats.fields[kCHARCOUNT];
+}