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import struct
import sys
def readU32(contents, offset):
wordBytes = contents[offset:offset + 4]
return struct.unpack('>I', wordBytes)[0]
def readU16(contents, offset):
wordBytes = contents[offset:offset + 2]
return struct.unpack('>H', wordBytes)[0]
def checkChecksum(infile):
contents = infile.read()
if len(contents) % 4:
print 'File length is not a multiple of 4'
sum = 0
for offset in range(0, len(contents), 4):
sum += readU32(contents, offset)
while sum >= 2**32:
sum -= 2**32
print 'Sum of whole file: %x' % sum
numTables = readU16(contents, 4)
for offset in range(12, 12 + numTables * 16, 16):
tag = contents[offset:offset + 4]
chksum = readU32(contents, offset + 4)
toffset = readU32(contents, offset + 8)
tlength = readU32(contents, offset + 12)
sum = 0
for offset2 in range(toffset, toffset + tlength, 4):
sum += readU32(contents, offset2)
while sum >= 2**32:
sum -= 2**32
if sum != chksum:
print 'Bad chksum: %s' % tag
if __name__ == '__main__':
if len(sys.argv) != 2:
print 'Usage: %s <ttf filename>' % sys.argv[0]
else:
checkChecksum(file(sys.argv[1], 'r'))
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