Difference between revisions of "BEAR4 compression"
From ScienceZero
(Created page with ' WORK IN PROGRESS... Category:Computing') |
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WORK IN PROGRESS... | WORK IN PROGRESS... | ||
| + | BEAR4 is designed for microcontrollers that have 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 index/count range. | ||
| + | |||
| + | Header | ||
| + | BE4R - file ID | ||
| + | w - word size (1-64) | ||
| + | s - symbol size (1-64) | ||
| + | h - symbol shift (0-63) | ||
| + | i - maximum index size (1-32) | ||
| + | c - maximum count size (1-16) | ||
| + | |||
| + | Data | ||
| + | 0 <symbol> | ||
| + | 1 <index> <count> | ||
| + | |||
| + | Pseudocode | ||
| + | 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 | ||
| + | |||
| + | |||
[[Category:Computing]] | [[Category:Computing]] | ||
Latest revision as of 16:46, 4 February 2016
WORK IN PROGRESS...
BEAR4 is designed for microcontrollers that have 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 index/count range.
Header
BE4R - file ID
w - word size (1-64)
s - symbol size (1-64)
h - symbol shift (0-63)
i - maximum index size (1-32)
c - maximum count size (1-16)
Data
0 <symbol> 1 <index> <count>
Pseudocode
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
