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rdp4mppc.py
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#!/usr/bin/python
# MPPC-Based Bulk Data Compression for RDP 4.0
# History size: 8192 bytes
# output is None if the output size is larger than input
# modified from https://github.com/parc-ccnx-archive/CCNxz/blob/master/mppc.py
import array
class RDP4MPPC(object):
HISTORY_SIZE = 8192
# Used as bit patterns in Offset Encoding (RFC2118 Sec 4.2.1)
__offset_pattern_64 = 0b1111
__offset_pattern_320 = 0b1110
__offset_pattern_8191 = 0b110
__length_pattern_3 = 0b0
__length_pattern_8 = 0b10
__length_pattern_16 = 0b110
__length_pattern_32 = 0b1110
__length_pattern_64 = 0b11110
__length_pattern_128 = 0b111110
__length_pattern_256 = 0b1111110
__length_pattern_512 = 0b11111110
__length_pattern_1024 = 0b111111110
__length_pattern_2048 = 0b1111111110
__length_pattern_4096 = 0b11111111110
__length_pattern_8192 = 0b111111111110
def __init__(self):
self.__in = None
self.__inOffset = 0
self.__out = None
self.__outByte = 0
self.__outBit = 0 # 0-7
self.__history = bytearray(RDP4MPPC.HISTORY_SIZE)
self.__historyOffset = 0
def __setInData(self, data):
self.__in = bytearray(data)
self.__inOffset = 0
# output size cannot be larger than input. input size is limited by HISTORY_SIZE
self.__out = bytearray(RDP4MPPC.HISTORY_SIZE)
self.__outByte = 0
self.__outBit = 0
self.__historyOffset = 0
def __findLongestHistory(self):
longestLen = 0
longestOffset = 0
searchPos = 0
history = self.__history
historyOffset = self.__historyOffset
data = self.__in[self.__inOffset:]
firstVal = data[0:1] # to make compatible on python 2 and 3
searchPos = history.find(firstVal, 0, historyOffset)
while searchPos != -1:
# fill history array while matching
history[historyOffset] = data[0]
matchLen = 1
while matchLen < len(data) and data[matchLen] == history[searchPos+matchLen]:
history[historyOffset+matchLen] = data[matchLen]
matchLen += 1
if matchLen >= longestLen:
longestLen = matchLen
longestOffset = searchPos
searchPos = history.find(firstVal, searchPos+1, historyOffset)
if longestLen > 2:
#print("Found longest match (off = {}, len = {})".format(longestOffset, longestLen))
return (longestOffset, longestLen)
else:
return (None, None)
def __pushByteToHistory(self, byte):
self.__history[self.__historyOffset] = byte
self.__historyOffset += 1
def __encode7bitLiteral(self, byte):
byte_offset = self.__outByte
bit_offset = self.__outBit
if bit_offset == 0:
self.__out[byte_offset] = byte
else:
self.__out[byte_offset] |= byte >> bit_offset
self.__out[byte_offset+1] = (byte << (8 - bit_offset)) & 0xff
self.__outByte += 1
def __encodeLiteral(self):
byte = self.__in[self.__inOffset]
self.__inOffset += 1
if byte < 0x80:
self.__encode7bitLiteral(byte)
else:
# write a "1" bit, then write the byte as a 7-bit literal
self.__out[self.__outByte] |= 1 << (7 - self.__outBit)
if self.__outBit == 7:
self.__outByte += 1
self.__outBit = 0
else:
self.__outBit += 1
self.__encode7bitLiteral(byte & 0x7F)
self.__pushByteToHistory(byte)
def __encodebits(self, bits, bit_length):
bit_offset = self.__outBit
available_bits = 8 - bit_offset
if bit_length <= available_bits:
# we can fit the whole thing, shift the bits
# up so we pack the top of the byte first
shift = available_bits - bit_length
x = bits << shift
self.__out[self.__outByte] |= x
self.__outBit += bit_length
if self.__outBit == 8:
self.__outByte += 1
self.__outBit = 0
else:
# grab 'available_bits' from the top
shift = bit_length - available_bits
self.__encodebits(bits >> shift, available_bits)
bit_length -= available_bits
mask = (1 << bit_length) - 1
bits &= mask
self.__encodebits(bits, bit_length)
def __encodeTupleOffset(self, offset):
if offset < 64:
# Encoded as '1111' plus lower 6 bits
self.__encodebits(RDP4MPPC.__offset_pattern_64, 4)
self.__encodebits(offset, 6)
elif offset < 320:
# Encoded as '1110' plus lower 8 bits of (value - 64)
self.__encodebits(RDP4MPPC.__offset_pattern_320, 4)
self.__encodebits(offset - 64, 8)
else:
# Encoded as '110' followed by lower 13 bits of (value - 320)
self.__encodebits(RDP4MPPC.__offset_pattern_8191, 3)
self.__encodebits(offset - 320, 13)
def __encodeTupleLength(self, length):
if length == 3:
self.__encodebits(RDP4MPPC.__length_pattern_3, 1)
elif length < 8:
self.__encodebits(RDP4MPPC.__length_pattern_8, 2)
self.__encodebits(length & 0x0003, 2)
elif length < 16:
self.__encodebits(RDP4MPPC.__length_pattern_16, 3)
self.__encodebits(length & 0x0007, 3)
elif length < 32:
self.__encodebits(RDP4MPPC.__length_pattern_32, 4)
self.__encodebits(length & 0x000F, 4)
elif length < 64:
self.__encodebits(RDP4MPPC.__length_pattern_64, 5)
self.__encodebits(length & 0x001F, 5)
elif length < 128:
self.__encodebits(RDP4MPPC.__length_pattern_128, 6)
self.__encodebits(length & 0x003F, 6)
elif length < 256:
self.__encodebits(RDP4MPPC.__length_pattern_256, 7)
self.__encodebits(length & 0x007F, 7)
elif length < 512:
self.__encodebits(RDP4MPPC.__length_pattern_512, 8)
self.__encodebits(length & 0x00FF, 8)
elif length < 1024:
self.__encodebits(RDP4MPPC.__length_pattern_1024, 9)
self.__encodebits(length & 0x01FF, 9)
elif length < 2048:
self.__encodebits(RDP4MPPC.__length_pattern_2048, 10)
self.__encodebits(length & 0x03FF, 10)
elif length < 4096:
self.__encodebits(RDP4MPPC.__length_pattern_4096, 11)
self.__encodebits(length & 0x07FF, 11)
else:
self.__encodebits(RDP4MPPC.__length_pattern_8192, 12)
self.__encodebits(length & 0x0FFF, 12)
def __encodeCopyTuple(self, offset, length):
self.__encodeTupleOffset(self.__historyOffset - offset)
self.__encodeTupleLength(length)
endOffset = self.__inOffset + length
while self.__inOffset < endOffset:
byte = self.__in[self.__inOffset]
self.__pushByteToHistory(byte)
self.__inOffset += 1
def __getOutput(self):
outSize = self.__outByte
if self.__outBit != 0:
# +1 because we need the length including the last byte
outSize += 1
#print("outSize = {}".format(outSize))
if outSize >= len(self.__in):
return None
return bytes(self.__out[:outSize])
@property
def history(self):
return self.__history
def compress(self, data):
if len(data) > RDP4MPPC.HISTORY_SIZE:
return None
self.__setInData(data)
while self.__inOffset < len(data):
(longestOffset, longestLen) = self.__findLongestHistory()
if longestOffset is None:
self.__encodeLiteral()
else:
self.__encodeCopyTuple(longestOffset, longestLen)
return self.__getOutput()