gen-cksum

#!/usr/bin/python
# Written by TravistyOJ

import sys, struct

if len(sys.argv) != 2:
    print "Usage: %s <filename>" % sys.argv[0]
else:
    with open(sys.argv[1], 'r+b') as rom:
        rom.seek(0x18E)
        curr_cksum = struct.unpack('>H', rom.read(2))[0]
        rom.seek(0x200)
        calc_cksum = 0
        while True:
            word = rom.read(2)
            if not word: break
            calc_cksum += struct.unpack('>H', word)[0]
        calc_cksum &= 0xffff
        print "Found checksum: %s" % hex(curr_cksum)
        print "Calcd checksum: %s" % hex(calc_cksum)
        if curr_cksum == calc_cksum:
            print "Checksum correct!"
        else:
            rom.seek(0x18E)
            rom.write(struct.pack('>H', calc_cksum))
            print "Checksum fixed!"