A collection of decoders for various modern variants of Lempel-Ziv style compression targeting the Super Famicom/Nintendo system. Written for the ca65 assembler, but should be easy to port to other assemblers.
Common characteristics:
- Designed for speed over code size
- Designed to run from ROM – no self-modifying code
- Full 24-bit addresses for source and destination can be freely set at the call site
- Uses DMA registers for temporary variables allowing for faster access than RAM
- Uses DMA to copy literal strings
- The compressed data or the decompression buffer may not cross bank boundaries
Statistics (speeds in KB/s on a Super Nintendo @ 3.58MHz):
LZ4 Mean Median Min Max
Ratio 2.603 2.308 1.741 7.334
Speed 209.377 186.633 137.775 403.959
LZSA1 Mean Median Min Max
Ratio 2.810 2.433 1.891 8.266
Speed 198.097 176.605 135.100 398.657
LZSA2 Mean Median Min Max
Ratio 3.040 2.651 2.117 8.551
Speed 144.596 121.368 96.250 349.974
ZX0 Mean Median Min Max
Ratio 3.217 2.718 2.176 9.799
Speed 100.045 83.592 61.838 270.151
LZ4 aims to achieve extremely fast decompression speeds, with a block format that trades size for simplicity.
LZSAv1 achieves better compression than LZ4 while still being almost as efficient to decode on 8-bit CPUs.
An excellent choice if you want fast decompression.
LZSAv2 achieves better compression than LZSAv1 while still being fairly efficient to decode on 8-bit CPUs. Of the decompressors included in this collection it has the largest code size, which is due to the somewhat involved block format.
Between the faster decompression of LZSA1 and the better compression ratio of ZX0, there is little reason to choose this algorithm.
ZX0 has the best compression ratio of the schemes included in this collection, which is achieved by encoding the length/match tokens in an interlaced Elias gamma coded bit stream. The bit twiddling involved accounts for the slower speed compared to the pure byte aligned (nibble in the case of LZSA2) accesses needed by the other decompressors.
That said it is still quite fast, and should be the clear choice if good compression ratio is the priority. It also has the smallest code size of the included decompressors.
- Improve test data set
- Add optional bank crossing ability
- lz4ultra compressor by Emmanuel Marty
- lzsa compressor by Emmanuel Marty
- salvador compressor by Emmanuel Marty
- ca65 and ld65 from the cc65 development package
- Mesen by Sour (for running tests and benchmarks)
All dependencies except Mesen are included in this repository.
SHVC-LZ is developed by David Lindecrantz and distributed under the terms of the MIT license.