altera_compress.py

#!/usr/bin/env python3

import sys

# pip3 install bitstring
from bitstring import BitArray, BitStream

def flip_nibbles(ibb):
	obb = bytearray(ibb)
	for i in range(len(ibb)):
		ib = ibb[i]
		in0 = ib & 0xF
		in1 = (ib & 0xF0) >> 4
		ob = (in0 << 4) | in1
		obb[i] = ob
	return obb

# works
def comp(in_bytes):
	# if len(in_bytes) % 2 == 1:
	# 	in_bytes += b'\xff'
	outbs = BitStream()
	outflagbs = BitStream()
	last_word_idx = 0
	for word_idx in range(len(in_bytes)//2):
		word = int.from_bytes(in_bytes[word_idx*2:(word_idx+1)*2], byteorder='little')
		# print('word: {:04x}'.format(word))
		flag_bits = 0

		n0 = (word & 0x000F) >> 0
		n1 = (word & 0x00F0) >> 4
		n2 = (word & 0x0F00) >> 8
		n3 = (word & 0xF000) >> 12

		comp_word = BitStream()


		(n0, n1, n2, n3) = (n0, n1, n2, n3)

		if n0 != 0:
			# print('n0 {:x}'.format(n0))
			flag_bits |= 0b0001
			comp_word += BitStream(uint=n0, length=4)
		if n1 != 0:
			# print('n1 {:x}'.format(n1))
			flag_bits |= 0b0010
			comp_word += BitStream(uint=n1, length=4)
		if n2 != 0:
			# print('n2 {:x}'.format(n2))
			flag_bits |= 0b0100
			comp_word += BitStream(uint=n2, length=4)
		if n3 != 0:
			# print('n3 {:x}'.format(n3))
			flag_bits |= 0b1000
			comp_word += BitStream(uint=n3, length=4)
		# print('flag_bits: {:04b} {:x}'.format(flag_bits, flag_bits))
		# if flag_bits != 0xF:
		# 	flag_bits += 1
		outbs += BitStream(uint=flag_bits, length=4)
		outbs += comp_word
		# outbs += BitStream(uint=flag_bits, length=4)
		outflagbs += BitStream(uint=1, length=4)
		if len(comp_word) > 0:
			outflagbs += BitStream(int=0, length=len(comp_word))
		# outflagbs += BitStream(uint=1, length=4)
		# if len(comp_word) == 0:
		# 	print('zero comp word')
		last_word_idx = word_idx
	print('last_word_idx: {} *2: {} len(in_bytes): {}'.format(last_word_idx, last_word_idx*2, len(in_bytes)))
	# if len(outbs) % 8 != 0:
	# 	rem = 8 - (len(outbs) % 8)
	# 	outbs += BitStream(uint=0, length=rem)
	# 	outflagbs += BitStream(uint=0, length=rem)
	if len(outbs) % 8 != 0:
		rem = 8 - (len(outbs) % 8)
		outbs += BitStream(int=0, length=rem)
		outflagbs += BitStream(uint=0, length=rem)
	return (outbs.bytes, outflagbs.bytes)

# broken
def comp2(in_bytes):
	ibs = BitStream(bytes=in_bytes)
	# ibs = ibs[4:]
	outbs = BitStream()
	for wordi in range(len(in_bytes)//2):
		flag_bits = 0
		comp_word = BitStream()
		for i in range(4):
		# for i in range(3,-1,-1):
			biti = wordi*16+4*i
			nib = ibs[biti:biti+4]
			# print('len {}'.format(len(nib)))
			# fb = 1 << (3 - i)
			fb = 1 << i
			if nib.any('1'):
				flag_bits |= fb
				comp_word += nib
			print('wordi: {} biti: {} nib: {:01x} i: {} fb: {:04b} {:01x} flag_bits: {:04b} {:01x}'.format(wordi, biti, nib.uint, i, fb, fb, flag_bits, flag_bits))
		outbs += BitStream(uint=flag_bits, length=4)
		outbs += comp_word

	if len(outbs) % 8 != 0:
		outbs += BitStream(uint=0, length=1) * (8 - (len(outbs) % 8))
	return outbs.bytes

inbuf = open(sys.argv[1], 'rb').read()


(outbuf, outflagsbuf) = comp(inbuf)
outbuf += b'\xff\xff' # HACK haven't figured out padding/alignment
outbuf = flip_nibbles(outbuf)
open(sys.argv[2], 'wb').write(outbuf)
open('flag-nibble-locs.bin', 'wb').write(outflagsbuf)

altera_decompress.py

#!/usr/bin/env python3

import sys

# pip3 install bitstring
from bitstring import BitArray, BitStream

def flip_nibbles(ibb):
	obb = bytearray(ibb)
	for i in range(len(ibb)):
		ib = ibb[i]
		in0 = ib & 0xF
		in1 = (ib & 0xF0) >> 4
		ob = (in0 << 4) | in1
		obb[i] = ob
	return obb

n_flag_bits = 4
n_bits_per_element = 4

def decomp2(in_bytes):
	ibs = BitStream(bytes=in_bytes)
	outbs = BitStream()
	i = 0
	while len(ibs) > 0:
		flag_bits = ibs[:n_flag_bits]
		del ibs[:n_flag_bits]
		flag_bits.reverse()
		for j, b in enumerate(flag_bits):
			if b:
				outbs += ibs[:n_bits_per_element]
				del ibs[:n_bits_per_element]
			else:
				outbs += BitStream(uint=0, length=n_bits_per_element)
		i += 1
	if len(outbs) % 8 != 0:
		outbs += BitStream(uint=0, length=(8 - (len(outbs) % 8)))
	return flip_nibbles(outbs.bytes)

inbuf = open(sys.argv[1], 'rb').read()

inbuf = flip_nibbles(inbuf)
outbuf = decomp2(inbuf)
open(sys.argv[2], 'wb').write(outbuf)