lz4 decompression in Python 2.x

lz4.py

# Warning: this implementation doesn't check if writes or reads will happen
# out of input/output buffer range, so that will generate IndexError exception

def LZ4_decompress(source, osize):
  isize = len(source)

  src = bytearray(source)
  dst = bytearray(osize)

  si = 0
  di = 0

  while True:
    token = src[si]
    si += 1

    literals = token >> 4
    match = token & 0xF

    if literals > 0:
      # process literal section
      if literals == 15:
        while src[si] == 255:
          literals += 255
          si += 1
        literals += src[si]
        si += 1

      dst[di:di+literals] = src[si:si+literals]
      di += literals
      si += literals

      # lz4 data can end only with block that has literals and has no match copy
      if si == len(src):
        break

    # process match copy section
    offset = src[si] + (src[si+1] << 8)
    si += 2
    assert offset != 0, "this doesn't make sense, offset=0 means this must be literal"

    if match == 15:
      while src[si] == 255:
        match += 255
        si += 1
      match += src[si]
      si += 1
    
    match += 4

    # use faster copy using slicing if possible
    # it can be used only when di - offset + match <= di
    if match <= offset:
      # fast copy
      dst[di:di+match] = dst[di-offset:di-offset+match]
    else:
      # slower copy
      for i in xrange(match):
        dst[di+i] = dst[di-offset+i]
    
    di += match

  return str(dst)