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#!/usr/bin/env python3
#
# This is free and unencumbered software released into the public domain.
#
# Anyone is free to copy, modify, publish, use, compile, sell, or
# distribute this software, either in source code form or as a compiled
# binary, for any purpose, commercial or non-commercial, and by any
# means.
def make_int_bits(value, nbits):
bits = list()
for i in range(nbits-1, -1, -1):
bits.append((value & (1 << i)) != 0)
return bits
def ice_compress(inbits):
outbits = list()
outbits += make_int_bits(0x49434543, 32)
outbits += make_int_bits(0x4f4d5052, 32)
deltas = list()
numzeros = 0
for bit in inbits:
if bit:
deltas.append(numzeros)
numzeros = 0
else:
numzeros += 1
i = 0
while i < len(deltas):
raw_len = 0
compr_len = 0
best_compr_raw_diff = -1
best_compr_raw_idx = -1
best_compr_raw_len = -1
for j in range(len(deltas) - i):
delta = deltas[i+j]
raw_len += delta + 1
if delta < 4:
compr_len += 3
elif delta < 32:
compr_len += 7
elif delta < 256:
compr_len += 11
else:
compr_len += 26
if compr_len - raw_len < max(best_compr_raw_diff - 4, 0) or raw_len > 64:
break
if compr_len - raw_len > best_compr_raw_diff:
best_compr_raw_diff = compr_len - raw_len
best_compr_raw_idx = j
best_compr_raw_len = raw_len
if best_compr_raw_diff > 9:
outbits.append(False)
outbits.append(False)
outbits.append(False)
outbits.append(True)
outbits += make_int_bits(best_compr_raw_len-1, 6)
for j in range(0, best_compr_raw_idx+1):
delta = deltas[i+j]
for k in range(delta):
outbits.append(False)
if j < best_compr_raw_idx:
outbits.append(True)
i += best_compr_raw_idx + 1
continue
delta = deltas[i]
i += 1
if delta < 4:
outbits.append(True)
outbits += make_int_bits(delta, 2)
elif delta < 32:
outbits.append(False)
outbits.append(True)
outbits += make_int_bits(delta, 5)
elif delta < 256:
outbits.append(False)
outbits.append(False)
outbits.append(True)
outbits += make_int_bits(delta, 8)
else:
outbits.append(False)
outbits.append(False)
outbits.append(False)
outbits.append(False)
outbits.append(True)
outbits += make_int_bits(delta, 23)
outbits.append(False)
outbits.append(False)
outbits.append(False)
outbits.append(False)
outbits.append(False)
outbits += make_int_bits(numzeros, 23)
return outbits
# ------------------------------------------------------
# Usage example:
# python3 icecompr.py < example_8k.bin > example_8k.compr
import sys
inbits = list()
for byte in sys.stdin.buffer.read():
for i in range(7, -1, -1):
inbits.append((byte & (1 << i)) != 0)
outbits = ice_compress(inbits)
for i in range(0, len(outbits), 8):
byte = 0
for k in range(i, min(i+8, len(outbits))):
if outbits[k]: byte |= 1 << (7-(k-i))
sys.stdout.buffer.write(bytes([byte]))
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