Difference between revisions of "BEAR4 compression"

Revision as of 03:57, 20 February 2011

WORK IN PROGRESS...

BEAR4 is designed for microcontrollers that has little RAM. It uses the data decompressed so far as the dictionary, compared to typical LZ compression this decreases efficiency since the index range must be larger and the need for storing the count. Most of the loss is recovered by only reading the number of bits required for the current range.

Header

BEAR4 (used as file ID)
ssssss - symbol size (1-64) 
iiiii - maximum index size (1-32)
cccc - maximum count size (1-16)

0 <symbol>
1 <index> <count>

do
  indexSize = min(log2(decompressedSize), maximumIndexSize)
  countSize = min(indexSize, maximumCountSize)
  read classBit
  if classBit = 0 then
    read symbol
    output symbol
  else
    read index, count
    for each count
      read symbolFromDecompressed
      output symbol
    next
  endif
loop