#!/usr/local/bin/perl -w

# Fix checksums in an otherwise valid hex file.
#
# Usage: hexchksum < file.hex > fixedfile.hex

while (<>)
{
	chomp;
	$total = 0;
	$bytes = ((length) - 1) / 2;
	for ($i = 0; $i < $bytes-1; ++$i)
	{
		$hexval = substr ($_, 1+$i*2, 2);
		$total += hex ($hexval);
	}
	$chksum = hex(substr ($_, $bytes*2-1, 2));
	$mychksum = (0 - $total) % 256;
	if ($chksum != $mychksum)
	{
		$old = sprintf ("%2.2X", $chksum);
		$new = sprintf ("%2.2X", $mychksum);
		s/$old$/$new/;
		print;
	}
	else
	{
		print;
	}
	print "\n";
}