# Fibonacci Data Compression
# http://en.wikipedia.org/wiki/Fibonacci_coding
# (Max compressible file size: 2**32 bytes)
# FB - 201101274
import sys
import os
def encode_fib(n):
# Return string with Fibonacci encoding for n (n >= 1).
result = ""
if n >= 1:
a = 1
b = 1
c = a + b # next Fibonacci number
fibs = [b] # list of Fibonacci numbers, starting with F(2), each <= n
while n >= c:
fibs.append(c) # add next Fibonacci number to end of list
a = b
b = c
c = a + b
result = "1" # extra "1" at end
for fibnum in reversed(fibs):
if n >= fibnum:
n = n - fibnum
result = "1" + result
else:
result = "0" + result
return result
def byteWriter(bitStr, outputFile):
global bitStream
bitStream += bitStr
while len(bitStream) > 8: # write byte(s) if there are more then 8 bits
byteStr = bitStream[:8]
bitStream = bitStream[8:]
outputFile.write(chr(int(byteStr, 2)))
def bitReader(n): # number of bits to read
global byteArr
global bitPosition
bitStr = ''
for i in range(n):
bitPosInByte = 7 - (bitPosition % 8)
bytePosition = int(bitPosition / 8)
byteVal = byteArr[bytePosition]
bitVal = int(byteVal / (2 ** bitPosInByte)) % 2
bitStr += str(bitVal)
bitPosition += 1 # prepare to read the next bit
return bitStr
# MAIN
if len(sys.argv) != 4:
print 'Usage: Fibonacci.py [e|d] [path]InputFileName [path]OutputFileName'
sys.exit()
mode = sys.argv[1] # encoding/decoding
inputFile = sys.argv[2]
outputFile = sys.argv[3]
# read the whole input file into a byte array
fileSize = os.path.getsize(inputFile)
fi = open(inputFile, 'rb')
# byteArr = map(ord, fi.read(fileSize))
byteArr = bytearray(fi.read(fileSize))
fi.close()
fileSize = len(byteArr)
print 'File size in bytes:', fileSize
print
if mode == 'e': # FILE ENCODING
# calculate the total number of each byte value in the file
freqList = [0] * 256
for b in byteArr:
freqList[b] += 1
# create a list of (frequency, byteValue, encodingBitStr) tuples
tupleList = []
for b in range(256):
if freqList[b] > 0:
tupleList.append((freqList[b], b, ''))
# sort the list according to the frequencies descending
tupleList = sorted(tupleList, key=lambda tup: tup[0], reverse = True)
# assign encoding bit strings to each byte value
for b in range(len(tupleList)):
tupleList[b] = (tupleList[b][0], tupleList[b][1], encode_fib(b + 1))
# print 'The list of (frequency, byteValue, encodingBitStr) tuples:'
# print tupleList
# print
# write the list of byte values as the compressed file header
bitStream = '' # global
fo = open(outputFile, 'wb')
fo.write(chr(len(tupleList) - 1)) # first write the number of byte values
for (freq, byteValue, encodingBitStr) in tupleList:
# convert the byteValue into 8-bit and send to be written into file
# bitStr = bin(byteValue)
# bitStr = bitStr[2:] # remove 0b
# bitStr = '0' * (8 - len(bitStr)) + bitStr # add 0's if needed for 8 bits
# byteWriter(bitStr, fo)
fo.write(chr(byteValue)) # this would do the same
# write 32-bit (input file size)-1 value
bitStr = bin(fileSize - 1)
bitStr = bitStr[2:] # remove 0b
bitStr = '0' * (32 - len(bitStr)) + bitStr # add 0's if needed for 32 bits
byteWriter(bitStr, fo)
# create a dictionary of byteValue : encodingBitStr pairs
dic = dict([(tup[1], tup[2]) for tup in tupleList])
# del tupleList
# print 'The dictionary of byteValue : encodingBitStr pairs:'
# print dic
# write the encoded data
for b in byteArr:
byteWriter(dic[b], fo)
byteWriter('0' * 8, fo) # to write the last remaining bits (if any)
fo.close()
elif mode == 'd': # FILE DECODING
bitPosition = 0 # global
n = int(bitReader(8), 2) + 1 # first read the number of byte values
# print 'Number of byte values:', n
dic = dict()
for i in range(n):
# read the byteValue
byteValue = int(bitReader(8), 2)
encodingBitStr = encode_fib(i + 1)
dic[encodingBitStr] = byteValue # add to the dictionary
# print 'The dictionary of encodingBitStr : byteValue pairs:'
# print dic
# print
# read 32-bit file size (number of encoded bytes) value
numBytes = long(bitReader(32), 2) + 1
print 'Number of bytes to decode:', numBytes
# read the encoded data, decode it, write into the output file
fo = open(outputFile, 'wb')
for b in range(numBytes):
# read bits until a decoding match is found
encodingBitStr = ''
while True:
encodingBitStr += bitReader(1)
# if encodingBitStr in dic:
if encodingBitStr.endswith('11'):
byteValue = dic[encodingBitStr]
fo.write(chr(byteValue))
break
fo.close()
