check-bytes.py

#!/usr/bin/env python

import sys

bs = 1024 * 1024

zero = '\x00'
one = '\xFF'

count = 0
f = open(sys.argv[1], "rb")
if sys.argv[2] == 'zero':
    target = zero
elif sys.argv[2] == 'one':
    target = one
else:
    raise Exception("must specify 'one' or 'zero'")
maxcount = int(sys.argv[3])

last_pos = None
while True:
    block = f.read(bs)
    if len(block) == 0:
	break
    elif count >= maxcount:
        break
    elif block != target * bs:
	for i in xrange(len(block)):
            pos = (count * bs) + i
            byte = block[i]
            if byte != target:
                if last_pos is None:
                    print pos, repr(byte)
                else:
                    print pos, repr(byte), "(+%i)" % (pos - last_pos)
                last_pos = pos
    count += 1