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#

# Decompression application using static arithmetic coding

#

# Usage: python arithmetic-decompress.py InputFile OutputFile

# This decompresses files generated by the arithmetic-compress.py application.

#

# Copyright (c) Project Nayuki

#

# https://www.nayuki.io/page/reference-arithmetic-coding

# https://github.com/nayuki/Reference-arithmetic-coding

#

import sys

import arithmeticcoding

python3 = sys.version_info.major >= 3

# Command line main application function.

def main(args):

# Handle command line arguments

if len(args) != 2:

sys.exit("Usage: python arithmetic-decompress.py InputFile OutputFile")

inputfile, outputfile = args

# Perform file decompression

with open(outputfile, "wb") as out, open(inputfile, "rb") as inp:

bitin = arithmeticcoding.BitInputStream(inp)

freqs = read_frequencies(bitin)

decompress(freqs, bitin, out)

def read_frequencies(bitin):

def read_int(n):

result = 0

for _ in range(n):

result = (result << 1) | bitin.read_no_eof() # Big endian

return result

freqs = [read_int(32) for _ in range(256)]

freqs.append(1) # EOF symbol

return arithmeticcoding.SimpleFrequencyTable(freqs)

def decompress(freqs, bitin, out):

dec = arithmeticcoding.ArithmeticDecoder(32, bitin)

while True:

symbol = dec.read(freqs)

if symbol == 256: # EOF symbol

break

out.write(bytes((symbol,)) if python3 else chr(symbol))

# Main launcher

if __name__ == "__main__":

main(sys.argv[1 : ])