54 lines
906 B
Python
54 lines
906 B
Python
from __future__ import print_function
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import sys
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def calc_checksum(data, old):
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a = 0
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c = 0
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for b in data:
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a = a + b + c
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c = 0
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if a > 255:
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a = a - 256
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c = 1
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if not old:
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a += c
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return a
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def usage():
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print("Usage: python checksum.py {--old|--new} <file.bin> [<checksum> <offset>]")
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exit(1)
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# main
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if len(sys.argv) != 3 and len(sys.argv) != 5:
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usage()
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if sys.argv[1] == "--old":
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old = True
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elif sys.argv[1] == "--new":
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old = False
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else:
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usage()
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filename = sys.argv[2]
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data = bytearray(open(filename, 'rb').read())
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checksum = calc_checksum(data, old)
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if len(sys.argv) != 5:
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print(filename + ": " + hex(checksum))
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exit(0)
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desired_checksum = int(sys.argv[3], 16)
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offset = int(sys.argv[4], 16)
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if checksum < desired_checksum:
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data[offset] = desired_checksum - checksum
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else:
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data[offset] = 0xff - (checksum - desired_checksum)
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file = open(filename, "wb")
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file.write(data)
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