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August 19, 2023 16:15
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| import zlib | |
| from io import BytesIO | |
| # TODO: make this shorter | |
| RLEFLATE_MAGIC = b'\xed\xe3\t\x90$I\x92$I\xcc\xff\xff\xff\xff\xff\xff\xff\xff'\ | |
| b'\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff'\ | |
| b'\xff\xff\xff\xff?3333\xe1\x0e\x00\x0e``\xa0\xaa*"\xc2\xdc]U\x04\x00\x80' | |
| RLEFLATE_EOF = b'\x77' | |
| RLEFLATE_REPEAT = [ | |
| None, b'W', b'7', b'G', b'g', b'#', b'3', b'+', b';', b'\x11', b'Q', | |
| b'\x19', b'Y', b'\x15', b'U', b'\x1d', b']', b'\n', b'*', b'J', b'j', | |
| b'\x0e', b'.', b'N', b'n', b'\xf7\x0b', b'\xf7+', b'\xf7K', b'\xf7k', | |
| b'\xf7\x0f', b'\xf7/', b'\xf7O', b'\xf7o', b'\xf7\x04', b'\xf7\x14', | |
| b'\xf7$', b'\xf74', b'\xf7D', b'\xf7T', b'\xf7d', b'\xf7t', b'\xf7\x06', | |
| b'\xf7\x16', b'\xf7&', b'\xf76', b'\xf7F', b'\xf7V', b'\xf7f', b'\xf7v', | |
| b'\xf7\x05', b'\xf7\x15', b'\xf7%', b'\xf75', b'\xf7E', b'\xf7U', b'\xf7e', | |
| b'\xf7u', b'\x04', b'\x14', b'$', b'4', b'D', b'T', b'd', b't' | |
| ] | |
| RLEFLATE_REPEAT_PREFIX = b'\xf7' | |
| # Yes, this really is faster than bit twiddling... | |
| def bitrev_u8(n): | |
| return int(f"{n:08b}"[::-1], 2) | |
| def encode_literal_pair(a, b): | |
| tmp = bitrev_u8(a) | |
| return bytes([ | |
| 0x0f | ((tmp << 4) & 0xf0), | |
| 0xf0 | (tmp >> 4), | |
| bitrev_u8(b) | |
| ]) | |
| def rledeflate(data): | |
| out = RLEFLATE_MAGIC | |
| i = 0 | |
| while i + 3 < len(data): | |
| runlen = 0 | |
| while data[i-4:i] == data[i+runlen*4:i+runlen*4+4] \ | |
| and runlen < 64 \ | |
| and i >= 4: | |
| runlen += 1 | |
| if runlen == 0: | |
| out += encode_literal_pair(data[i+0], data[i+1]) + \ | |
| encode_literal_pair(data[i+2], data[i+3]) | |
| i += 4 | |
| else: | |
| out += RLEFLATE_REPEAT[runlen] | |
| i += runlen * 4 | |
| remainder = len(data) - i | |
| if remainder >= 2: | |
| out += encode_literal_pair(data[i+0], data[i+1]) | |
| i += 2 | |
| remainder -= 2 | |
| # 1 byte left to output, EOF marker will straddle the last byte | |
| if remainder: | |
| tmp = bitrev_u8(data[i]) | |
| out += bytes([ | |
| 0x0f | ((tmp << 4) & 0xf0), | |
| 0x70 | (tmp >> 4), | |
| 0x07, # EOF | |
| ]) | |
| return out | |
| # we'll reach here on all even-length messages | |
| out += RLEFLATE_EOF | |
| return out | |
| def rleinflate(data): | |
| data = BytesIO(data) | |
| magic = data.read(len(RLEFLATE_MAGIC)) | |
| assert(magic == RLEFLATE_MAGIC) | |
| out = b"" | |
| while True: | |
| assert(tmp := data.read(1)) | |
| if tmp == RLEFLATE_EOF: | |
| return out | |
| if tmp[0] & 0x0f == 0x0f: | |
| next0 = data.read(1)[0] | |
| next1 = data.read(1)[0] | |
| out += bytes([bitrev_u8( | |
| (tmp[0] >> 4) | ((next0 << 4) & 0xF0) | |
| )]) | |
| if next0 & 0xf0 == 0x70: # EOF | |
| assert(next1 == 0x07) | |
| return out | |
| out += bytes([bitrev_u8(next1)]) | |
| continue | |
| if tmp == RLEFLATE_REPEAT_PREFIX: | |
| assert(next0 := data.read(1)) | |
| tmp += next0 | |
| repcount = RLEFLATE_REPEAT.index(tmp) | |
| assert(len(out) >= 4) | |
| out += out[-4:] * repcount | |
| def zlib_inflate(data): | |
| d = zlib.decompressobj(wbits=-15) | |
| return d.decompress(data) + d.flush(zlib.Z_FINISH) | |
| msg = b"Helloooooooooooooooooooooooooooooo, world!" + b"!" * 1000 | |
| compressed = rledeflate(msg) | |
| print(compressed) | |
| print("ratio:", len(compressed)/len(msg)) | |
| zlib_reinflated = zlib_inflate(compressed) | |
| print(zlib_reinflated) | |
| assert(msg == zlib_reinflated) | |
| rleinflated = rleinflate(compressed) | |
| print(rleinflated) | |
| assert(msg == rleinflated) | |
| assert(rleinflated == zlib_reinflated) |
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