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#!/usr/bin/env python3
# Usage: ./xor_compress.py sources.bin... > dest.bin.xor
import sys
data = bytearray()
for filename in sys.argv[1:]:
with open(filename, 'rb') as f:
data.extend(f.read())
n = len(data)
output = bytearray()
v = 0x00
i = 0
while i < n:
byte = data[i]
i += 1
if data[i] == v:
# Alternating (>= 0x80)
# Run stops at 0x80 bytes or when the values stop alternating
size = 0
while i < n and size < 0x80 and data[i] == (byte if size % 2 else v):
size += 1
i += 1
output.append(size + 0x7f)
output.append(v ^ byte)
if not size % 2:
v = byte
else:
# Sequential (< 0x80)
# Run stops at 0x80 bytes or when the value two ahead is equal to v
buffer = [v ^ byte]
while i < n:
v = byte
if len(buffer) > 0x7f or (i + 1 < n and data[i + 1] == v):
break
byte = data[i]
buffer.append(v ^ byte)
i += 1
output.append(len(buffer) - 1)
output.extend(buffer)
sys.stdout.buffer.write(output)
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