multi-bleu.perl

#!/usr/bin/perl -w

# $Id: multi-bleu.perl 1971 2009-01-08 00:47:10Z phkoehn $
use strict;

my $stem = $ARGV[0];
if (!defined $stem) {
  print STDERR "usage: multi-bleu.pl reference < hypothesis\n";
  print STDERR "Reads the references from reference or reference0, reference1, ...\n";
  exit(1);
}

my @REF;
my $ref=0;
while(-e "$stem$ref") {
    &add_to_ref("$stem$ref",\@REF);
    $ref++;
}
&add_to_ref($stem,\@REF) if -e $stem;

sub add_to_ref {
    my ($file,$REF) = @_;
    my $s=0;
    open(REF,$file) or die "Can't read $file";
    while(<REF>) {
	chop;
	push @{$$REF[$s++]}, $_;
    }
    close(REF);
}

my(@CORRECT,@TOTAL,$length_translation,$length_reference);
my $s=0;
while(<STDIN>) {
    chop;
    my @WORD = split;
    my %REF_NGRAM = ();
    my $length_translation_this_sentence = scalar(@WORD);
    my ($closest_diff,$closest_length) = (9999,9999);
    foreach my $reference (@{$REF[$s]}) {
#      print "$s $_ <=> $reference\n";
	my @WORD = split(/ /,$reference);
	my $length = scalar(@WORD);
        my $diff = abs($length_translation_this_sentence-$length);
	if ($diff < $closest_diff) {
	    $closest_diff = $diff;
	    $closest_length = $length;
	    # print STDERR "$s: closest diff ".abs($length_translation_this_sentence-$length)." = abs($length_translation_this_sentence-$length), setting len: $closest_length\n";
	} elsif ($diff == $closest_diff) {
            $closest_length = $length if $length < $closest_length;
            # from two references with the same closeness to me
            # take the *shorter* into account, not the "first" one.
        }
	for(my $n=1;$n<=4;$n++) {
	    my %REF_NGRAM_N = ();
	    for(my $start=0;$start<=$#WORD-($n-1);$start++) {
		my $ngram = "$n";
		for(my $w=0;$w<$n;$w++) {
		    $ngram .= " ".$WORD[$start+$w];
		}
		$REF_NGRAM_N{$ngram}++;
	    }
	    foreach my $ngram (keys %REF_NGRAM_N) {
		if (!defined($REF_NGRAM{$ngram}) || 
		    $REF_NGRAM{$ngram} < $REF_NGRAM_N{$ngram}) {
		    $REF_NGRAM{$ngram} = $REF_NGRAM_N{$ngram};
#	    print "$i: REF_NGRAM{$ngram} = $REF_NGRAM{$ngram}<BR>\n";
		}
	    }
	}
    }
    $length_translation += $length_translation_this_sentence;
    $length_reference += $closest_length;
    for(my $n=1;$n<=4;$n++) {
	my %T_NGRAM = ();
	for(my $start=0;$start<=$#WORD-($n-1);$start++) {
	    my $ngram = "$n";
	    for(my $w=0;$w<$n;$w++) {
		$ngram .= " ".$WORD[$start+$w];
	    }
	    $T_NGRAM{$ngram}++;
	}
	foreach my $ngram (keys %T_NGRAM) {
	    $ngram =~ /^(\d+) /;
	    my $n = $1;
            # my $corr = 0;
#	print "$i e $ngram $T_NGRAM{$ngram}<BR>\n";
	    $TOTAL[$n] += $T_NGRAM{$ngram};
	    if (defined($REF_NGRAM{$ngram})) {
		if ($REF_NGRAM{$ngram} >= $T_NGRAM{$ngram}) {
		    $CORRECT[$n] += $T_NGRAM{$ngram};
                    # $corr =  $T_NGRAM{$ngram};
#	    print "$i e correct1 $T_NGRAM{$ngram}<BR>\n";
		}
		else {
		    $CORRECT[$n] += $REF_NGRAM{$ngram};
                    # $corr =  $REF_NGRAM{$ngram};
#	    print "$i e correct2 $REF_NGRAM{$ngram}<BR>\n";
		}
	    }
            # $REF_NGRAM{$ngram} = 0 if !defined $REF_NGRAM{$ngram};
            # print STDERR "$ngram: {$s, $REF_NGRAM{$ngram}, $T_NGRAM{$ngram}, $corr}\n"
	}
    }
    $s++;
}
my $brevity_penalty = 1;
my $bleu = 0;

my @bleu=();

for(my $n=1;$n<=4;$n++) {
  if (defined ($TOTAL[$n])){
    $bleu[$n]=($TOTAL[$n])?$CORRECT[$n]/$TOTAL[$n]:0;
    # print STDERR "CORRECT[$n]:$CORRECT[$n] TOTAL[$n]:$TOTAL[$n]\n";
  }else{
    $bleu[$n]=0;
  }
}

if ($length_reference==0){
  printf "BLEU = 0, 0/0/0/0 (BP=0, ratio=0, hyp_len=0, ref_len=0)\n";
  exit(1);
}

if ($length_translation<$length_reference) {
  $brevity_penalty = exp(1-$length_reference/$length_translation);
}
$bleu = $brevity_penalty * exp((my_log( $bleu[1] ) +
				my_log( $bleu[2] ) +
				my_log( $bleu[3] ) +
				my_log( $bleu[4] ) ) / 4) ;
printf "BLEU = %.2f, %.1f/%.1f/%.1f/%.1f (BP=%.3f, ratio=%.3f, hyp_len=%d, ref_len=%d)\n",
    100*$bleu,
    100*$bleu[1],
    100*$bleu[2],
    100*$bleu[3],
    100*$bleu[4],
    $brevity_penalty,
    $length_translation / $length_reference,
    $length_translation,
    $length_reference;

sub my_log {
  return -9999999999 unless $_[0];
  return log($_[0]);
}