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encoder_init.py
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encoder_init.py
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import bitfile
import numpy as np
global EOF
global PRECISION
global MAX_symbol
global low
global high
global code
global underflow
global cum_prob
global output_file
global ranges
def init_en():
global EOF
global PRECISION
global MAX_symbol
global low
global high
global code
global underflow
global cum_prob
global output_file
global ranges
EOF = 256
PRECISION = 16
MAX_symbol=(1<<14)
low = 0
high = 0xFFFF
code = 0
underflow = 0
cum_prob = 0
output_file = None
ranges = []
def encode_data(input_list, output_file_name):
global EOF
global PRECISION
global MAX_symbol
global low
global high
global code
global underflow
global cum_prob
global output_file
global ranges
init_en()
probability_list(input_list) # create the probability of input list
output_file = bitfile.BitFile()
output_file.open(output_file_name,'wb')
for i in xrange(EOF+2):
prob = (ranges[i])
output_file.put_bits_ltom(prob,14) # write the probability of list
for c in input_list:
apply_symbol_range(c) # encode symbol c
write_encoded_bits()
apply_symbol_range(EOF) # encode the EOF symbol
write_encoded_bits()
write_remaining()
output_file.close()
def probability_list(data):
global cum_prob
global ranges
count_array = [0 for i in xrange(EOF)]
Symble = Counter(data)
for i,j in Symble.items():
count_array[i] = j
total_count = sum(count_array)
if total_count >= MAX_symbol:
rescale_value = (total_count / MAX_symbol) + 1
for index, value in enumerate(count_array):
if value > rescale_value:
count_array[index] = value / rescale_value
elif value != 0:
count_array[index] = 1
ranges = [0] + count_array + [1]
cum_prob = sum(count_array)+1
for c in xrange(EOF + 1):
ranges[c + 1] += ranges[c]
def Counter(data):
count = {}
for i in xrange(len(data)):
count[data[i]] = 0
for i in xrange(len(data)):
count[data[i]] += 1
return count
def apply_symbol_range(symbol):
global low
global high
Symbol_range = high - low + 1
high = low + ranges[symbol+1]* Symbol_range / cum_prob - 1
low = low + ranges[symbol]* Symbol_range / cum_prob
def write_encoded_bits():
global low
global high
global underflow
while True:
if (~high & 0x8000): # if high < 1/2*range ==> output 0
output_file.put_bit(0)
low <<= 1
high <<= 1
high |= 0x0001
while underflow > 0:
output_file.put_bit(1)
underflow -= 1
elif (low & 0x8000): # if low > 1/2*range ==> output 1
output_file.put_bit(1)
low <<= 1
high <<= 1
high |= 0x0001
while underflow > 0:
output_file.put_bit(0)
underflow -= 1
elif (~high & 0x4000) and (low & 0x4000): # if low >1/4*range and high < 3/4*range ==> underflow += 1
underflow += 1
low &= 0x3fff
low &= 0x7fff
low <<= 1
high |= 0x4000
high &= 0x7fff
high <<= 1
high |= 0x0001
else:
return
def write_remaining():
global underflow
output_file.put_bit((low & 0x4000) != 0)
underflow += 1
for i in xrange(underflow):
output_file.put_bit((low & 0x4000) == 0)