minor fixes to lzw_decode to increase clarity; tweaked to output format in testlzw

2 files changed, 12 insertions, 22 deletions

diff --git a/challenge-022/duncan-c-white/perl5/LZW.pm b/challenge-022/duncan-c-white/perl5/LZW.pm
index 5dac1ca36e..b2ff41a4e0 100644
--- a/challenge-022/duncan-c-white/perl5/LZW.pm
+++ b/challenge-022/duncan-c-white/perl5/LZW.pm
@@ -180,11 +180,9 @@ fun lzw_decode( $binstr )
 	my $ndict = @newdict;
 	print "decoding first $b, pos=$pos, ndict=$ndict\n" if $debug;
 
-
 	die "LZW_decode: first bin $b (pos $pos) not in dict, $ndict entries\n" unless $pos<$ndict;
 
 	my $prevf = $newdict[$pos];	# previous text fragment
-
 	my $result = $prevf;
 
 	while( $binstr )
@@ -199,30 +197,22 @@ fun lzw_decode( $binstr )
 
 		my $ndict = @newdict;
 
-		my $f;		# current decoded text fragment
+		die "decode: bad pos $pos (dictionary has $ndict ".
+		    "entries) result=$result, b=$b, ".
+		    "binstr=$binstr)\n" if $pos > $ndict;
 
-		# if pos in dict?
-		if( $pos < $ndict )
-		{
-			$f = $newdict[$pos];
-		} elsif( $pos == $ndict )
-		{
-			$f = $prevf . substr($prevf,0,1);
-		} else
-		{
-			die "decode: bad pos $pos (dictionary has $ndict ".
-			    "entries) result=$result, b=$b, ".
-			    "binstr=$binstr)\n";
-		}
+		my $f = $pos < $ndict ?    # current decoded text fragment
+				$newdict[$pos] :
+				$prevf . substr($prevf,0,1);
 
-		# ok, so $b represents text frag $f
+		# ok, so encoded $b represents decoded text frag $f
 		print "b $b, pos=$pos, prevf=$prevf, f=$f\n" if $debug;
 
 		$result .= $f;
 
-		# the next entry in the dictionary must be the WHOLE of
-		# the previous fragment plus the FIRST letter of the
-		# current fragment $f
+		# the next entry in the dictionary is the WHOLE of
+		# the previous fragment $prevf, plus the FIRST letter
+		# of the current fragment $f
 		my $new = $prevf . substr($f,0,1);
 
 		$pos = @newdict;
diff --git a/challenge-022/duncan-c-white/perl5/testlzw.pl b/challenge-022/duncan-c-white/perl5/testlzw.pl
index efb86814fc..ad80a147bf 100755
--- a/challenge-022/duncan-c-white/perl5/testlzw.pl
+++ b/challenge-022/duncan-c-white/perl5/testlzw.pl
@@ -50,11 +50,11 @@ foreach (1..$n)
 	my $text = make_random_string( $len );
 	my $binstr = lzw_encode( $text );
 	$text .= '#';
-	print "\ntext: $text\n";
+	print "text: $text\n";
 	#print "  encodes to: $binstr\n";
 	my $text2 = lzw_decode( $binstr );
 	#print "  which decodes to: $text2\n";
-	print "  encodes+decodes to: $text2\n" if 0;
+	#print "  encodes+decodes to: $text2\n";
 	die "text $text -> encodes to $binstr -> decodes to $text2\n"
 		unless $text eq $text2;
 }