bin/pidiff: position-independent diff filter

pidiff removes changes that merely move lines around from diff -u output.
The result is no longer a valid patch and is only intended for human use.

bin/pidiff

@@ -0,0 +1,97 @@
+#!/usr/bin/perl
+#
+# pidiff - Position-independent diff filter
+#
+# Copyright 2012 by Werner Almesberger
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+
+
+sub usage
+{
+	print STDERR <<'EOF'
+usage: diff -u ... | $0 [-n] [-D]
+
+  -n  print line numbers
+  -D  print debug output
+EOF
+;
+	exit(1);
+}
+
+
+while ($ARGV[0] =~ /^-/) {
+	if ($ARGV[0] eq "-n") {
+		$num = 1;
+	} elsif ($ARGV[0] eq "-D") {
+		$debug = 1;
+	} else {
+		&usage;
+	}
+	shift @ARGV;
+}
+
+$n = 0;
+while (<>) {
+	$n++;
+	next unless /^[-+]/;
+	if (/^-/) {
+		push @{ $m{$'} }, $n;
+	} else {
+		push @{ $p{$'} }, $n;
+	}
+}
+for $k (keys %p) {
+	undef $bm, $mp;
+	undef $bd;
+	$em = $#{ $m{$k} };
+	$ep = $#{ $p{$k} };
+	$m = 0;
+	$p = 0;
+	while ($m <= $em && $p <= $ep) {
+		$d = abs($m{$k}[$m]-$p{$k}[$p]);
+		($bm, $bp, $bd) = ($m, $p, $d)
+		    unless $d > $bd && defined $bd;
+		if ($m{$k}[$m] <= $p{$k}[$p] && $m < $em) {
+			$m++;
+		} else {
+			$p++;
+		}
+	}
+# older variant, less efficient
+#	for $m (0..$#{ $m{$k} }) {
+#		for $p (0..$#{ $m{$k} }) {
+#			$d = abs($m{$k}[$m]-$p{$k}[$p]);
+#			($bm, $bp, $bd) = ($m, $p, $d)
+#			    unless $d > $bd && defined $bd;
+#		}
+#	}
+	next unless defined $bd;
+	if ($debug) {
+		chop($kk = $k);
+		print STDERR
+		    "$kk: del m at $bm ($m{$k}[$bm]) p at $bp ($p{$k}[$bp])\n";
+	}
+	splice(@{ $m{$k} }, $bm, 1);
+	splice(@{ $p{$k} }, $bp, 1);
+	redo;
+}
+
+for $k (keys %m) {
+	for (@{ $m{$k} }) {
+		$l{$_} = "-$k"; 
+	}
+}
+for $k (keys %p) {
+	for (@{ $p{$k} }) {
+		$l{$_} = "+$k"; 
+	}
+}
+for (sort { $a <=> $b } keys %l) {
+	print "$_: " if $num;
+	print $l{$_};
+}