LZ11 decompression algo (based on https://gist.github.com/NWPlayer123/05dd55dd1cce6eb5457741ce14f48587)

lz11dec.py

from struct import pack, unpack
from os import remove, rename
import sys

do_replace = 1

with open(sys.argv[1], "rb") as f:
    name = sys.argv[1].split(".")
    name = ".".join(name[:-1]) + ".dec." + name[-1]
    with open(name, "wb+") as o:
        header = unpack("<I", f.read(4))[0]
        assert header & 0xFF == 0x11 #LZ11
        unc_size = header >> 8 #remove 0x11
        o.write("\x00" * unc_size) #pre-allocate
        o.seek(0);mask = 0
        while unc_size != 0:
            if not mask: #read new flag byte
                mask = 0x80
                flag = ord(f.read(1))
            if not flag & mask: #0, read one byte
                o.write(f.read(1))
                unc_size -= 1
            else: #1, RLE stuff
                byte1 = ord(f.read(1))
                length = byte1 >> 4
                if length == 0:
                    byte2 = ord(f.read(1))
                    byte3 = ord(f.read(1))
                    size = (((byte1 & 15) << 4) | (byte2 >> 4)) + 0x11
                    back = (((byte2 & 15) << 8) | byte3) + 1
                elif length == 1:
                    byte2 = ord(f.read(1))
                    byte3 = ord(f.read(1))
                    byte4 = ord(f.read(1))
                    size = (((byte1 & 15) << 12) | (byte2 << 4) | (byte3 >> 4)) + 0x111
                    back = (((byte3 & 15) << 8) | byte4) + 1
                else:
                    byte2 = ord(f.read(1))
                    size = (byte1 >> 4) + 1
                    back = (((byte1 & 15) << 8) | byte2) + 1
                    
                unc_size -= size
                if size > back: #overlap, cache it
                    o.seek(back * -1, 1)
                    buff = list(o.read(size + back))
                    for i in range(size):
                        buff[back + i] = buff[i]
                    o.seek((size + back) * -1, 1)
                    o.write("".join(buff))
                else:
                    o.seek(back * -1, 1)
                    data = o.read(size)
                    o.seek(back - size, 1)
                    o.write(data)
            mask >>= 1
if do_replace:
    remove(sys.argv[1])
    rename(name, sys.argv[1])