#!/usr/bin/python

import sys;

class Tool:

    def ROL(self, i, b):
        return ((i << b) | (i >> (32 - b))) & 0xffffffff

    def R4(self, b):
        return b[0]*0x1000000 + b[1]*0x10000 + b[2]*0x100 + b[3]

    def crc(self, f):
        seed = 0xdf26f436
        t1 = t2 = t3 = t4 = t5 = t6 = seed

        f.seek(0x0710 + 0x40)
        lookup = f.read(0x100)

        f.seek(0x1000)
        for i in range(0x1000, 0x101000, 4):
            d = self.R4(f.read(4))

            if ((t6 + d) & 0xffffffff) < t6:
                t4 += 1
                t4 &= 0xffffffff

            t6 += d
            t6 &= 0xffffffff

            t3 ^= d

            r = self.ROL(d, d & 0x1F)

            t5 += r
            t5 &= 0xffffffff

            if t2 > d:
                t2 ^= r
            else:
                t2 ^= t6 ^ d

            o = i & 0xFF
            temp = self.R4(lookup[o:o + 4])
            t1 += temp ^ d
            t1 &= 0xffffffff

        crc1 = t6 ^ t4 ^ t3
        crc2 = t5 ^ t2 ^ t1

        return crc1 & 0xffffffff, crc2 & 0xffffffff

fd = open(sys.argv[1], 'rb')

# Read existing CRC
fd.seek(0x10)
old = [
    int.from_bytes(fd.read(4), 'big'),
    int.from_bytes(fd.read(4), 'big'),
]

# Calculate new CRC
tool = Tool()
new = tool.crc(fd)
fd.close()

if '--verbose' in sys.argv:
    print('Old CRCs: %08x %08x' % (old[0], old[1]))
    print('New CRCs: %08x %08x' % (new[0], new[1]))

if new != old and '--write' in sys.argv:
    fd = open(sys.argv[1], 'r+b')
    fd.seek(0x10)
    fd.write(new[0].to_bytes(4, 'big'))
    fd.write(new[1].to_bytes(4, 'big'))
    fd.close()
