How to efficiently find where a patch applies?

In the past couple weeks, I have had several occasions where a collaborator has sent a patch, which does not have information about where the patch forked from master. I wrote the following scripts to try to discover where the patch should be applied. Is there a better way?

create_awk.pl:
----------------------->8------------------------------------------
#! /usr/bin/env perl
print <<HEADER;
BEGIN {
	i = 0
}
HEADER

print "/";

my $numseen=0;
my $nummatches = 0;
while(<STDIN>){
	if(/^index ([0-9a-f]+)\.\..+$/){
		$hash = $1;
	} else {
		next;
	}
	if($hash =~ /^0*$/) {
		next;
	}
	print "|" if($numseen > 0);
	$numseen = 1;
	++$nummatches;
	print "$hash";	
}
print "/{ i += 1; print \$0}\n";

print <<FOOTER;
END {
	if( i == $nummatches) {
		print "FOUND IT";
		exit 1;
	}
	print "i =",i;
	exit 0;
}
FOOTER
----------------------->8------------------------------------------

To find the place where the patch applies, I then would run something like

git rev-list --all | \
while read commit; do \
	git ls-tree -r $commit | \
	awk "$(perl ~/programs/git-hacks/create_awk.pl < <patch file>)" > /dev/null || \
	echo $commit; \
done

Nathan Panike