Decompression - marinus-lab/z88dk GitHub Wiki

z88dk provides a variety of decompression routines as part of the library covering a range of decompressors. These routines have been provided with C function wrappers and are callable from code compiled using both sccz80 and zsdcc.

A comparison of several z80 decompression algorithms can be found here; https://www.cpcwiki.eu/forum/programming/new-cruncher-zx0/msg197727/#msg197727, but can be roughly summarised as "use ZX0".

ROM data section compression

Both classic and newlib libraries support storing the data sections compressed in ROM and then expanding them into RAM. This behaviour is controlled by the CRT_MODEL pragma option;

  • CRT_MODEL=1 The data section is copied from ROM into RAM on program start.
  • CRT_MODEL=2 The data section is stored compressed in ROM and decompressed into RAM on program start. The compression used is zx7.
  • CRT_MODEL=3 The data section is stored compressed in ROM and decompressed into RAM on program start. The compression used is zx0.

ZX0 Decompression <compress/zx0.h>

Source site: https://github.com/einar-saukas/ZX0

Available: 8080, z80, z80n, Rabbit (not all variants available on 8080)

ZX0 is an optimal data compressor for a custom LZ77/LZSS based compression format, that provides a tradeoff between high compression ratio, and extremely simple fast decompression.

C wrappers, including __z88dk_callee variants are available for all of the decompressor variants include the +zx centric RCS routines for ZX Spectrum screens.

This is the recommended compression algorithm that new applications use.

ZX1 Decompression <compress/zx1.h>

Source site: https://github.com/einar-saukas/ZX1

Available: 8080, gbz80, z80, z80n, Rabbit (not all variants available on 8080 & gbz80)

ZX1 is a simpler but faster version of ZX0 that sacrifices about 1.5% compression to run about 15% faster.

C wrappers, including __z88dk_callee variants are available for all of the decompressor variants include the +zx centric RCS routines for ZX Spectrum screens.

The compression tool is not supplied with z88dk, so you'll need to download and compile it from the upstream site linked above.

ZX2 Decompression <compress/zx2.h>

Source site: https://github.com/einar-saukas/ZX2

Available: gbz80, z80, z80n, Rabbit

ZX2 is a minimalist version of ZX1. It's intended to help compressing programs and data blocks so small that saving a few bytes in the decompressor itself can make a difference (for instance to create 1Kb demos).

The compression tool is not supplied with z88dk, so you'll need to download and compile it from the upstream site linked above.

ZX7 Decompression <compress/zx7.h>

Source site: https://spectrumcomputing.co.uk/entry/27996/ZX-Spectrum/ZX7

Available: gbz80, z80, z80n, Rabbit (not all variants available on gbz80)

C wrappers, including __z88dk_callee variants are available for all of the decompressor variants include the +zx centric RCS routines for ZX Spectrum screens.

APLib Decompression <compress/aplib.h>

Available: 8080, gbz80, z80, z80n

APLib is a general-purpose compression library written by Jørgen Ibsen, based on his aPACK executable compressor.

This decompressor is particularly useful on the +sms platform due to the availability of a direct to VRAM decompressor.

PUCrunch Decompression <cpc.h>

PUCrunch decompression is available for +cpc only. The following function is provided:

void cpc_Uncrunch(void *src, void *dest)

This function is provided for legacy purposes only, and it is strongly recommended that new projects use one of the ZX decompressors.

Exomiser 2 Decompression <cpc.h>

Exomiser 2 decompression is available for +cpc only. The following function is provided:

void cpc_UnExo(void *src, void *dest)

This function is provided for legacy purposes only, and it isstrongly recommended that new projects use one of the ZX decompressors.

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