- [x] I have read and followed the [Contribution Guidelines](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/CONTRIBUTING.md#code-contributions).
- [x] I have read and followed the [AI Policy](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/docs/policies/AI.md)
- [x] I have read and followed the [Coding Guidelines](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/docs/policies/Coding.md) to the best of my ability.
-------------------
A new NSO compression method was introduced in Switch 22.0.0. This is a
customized variant of zstd and is used when NSO flags have bit 7 set.
Key characteristics:
- ZSTD_MAGICNUMBER is set to 0x4349425A (b'ZBIC') instead of 0xFD2FB528
- ZSTD_LEGACY_SUPPORT is set to 0
- ZSTD_TRACE is set to 1, zstd version used is 1.5.7 (10507)
- FSE_readNCount is replaced with a BIC (Binary Interpolative Coding)
version which improves compression of entropy tables significantly
Source: https://switchbrew.org/wiki/22.0.0
Implementation:
- Detect ZBIC segments via NSO flag bit 7 (NsoFlags_UseZbicCompression)
and/or ZBIC magic scan in nso.cpp
- Fall back to LZ4 when ZBIC is not detected or returns unexpected size
- Handle segment 0 alternate offset (0x100 vs 0x108) for both ZBIC and LZ4
References:
- Atmosphère loader/strat zstd-zbic integration:
082115187a
- nxdumptool ZBIC segment compression support:
441e5c0904
- STORM_SWITCH ZBIC implementation:
1e09eb82b7
Tested with firmware 23.0.0 and ZBIC-compressed NSOs.
Co-authored-by: xbzk <xbzk@eden-emu.dev>
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/4482
Reviewed-by: CamilleLaVey <camillelavey99@gmail.com>
Reviewed-by: lizzie <lizzie@eden-emu.dev>
Reviewed-by: Maufeat <sahyno1996@gmail.com>
815325ccec