Case study
Little Planet: Sonic CD recompiled from a matching disassembly
Disassembles every executable file on the Sonic CD disc from runtime coverage and recursive descent, reassembles them byte-identically, and translates the code statically to C on a from-scratch Mega-CD runtime that replaces the BIOS with a high-level implementation. Recompiled blocks run only where memory still holds the code they came from, and a script compares 96 stage runs frame by frame against the interpreter. The project also patches in widescreen and per-zone saves; results remain project-reported.
- Targets
- Game
- Category
- Independent reconstruction cases
- Relationship
- Independent reconstruction project
- Sources reviewed
Requirements & limits
- Prerequisites: Supply your own Sonic CD disc image (cue/bin, iso, ccd/img/sub, chd, or cue with compressed audio). The Japanese G-6021 release, identified by a data-track SHA-1 in README, is the tested one; other releases boot but are untested. No BIOS dump is needed, and no disc data is included.
- Prerequisites: Releases target Windows x64 (installer or portable zip), macOS 11+ (not notarized) and Linux x86_64/ARM64 AppImages. Source builds need Python (3.10+ on Windows) and SDL3, with Visual Studio 2022 Build Tools, Xcode command-line tools or gcc/g++. The optional remastered opening also needs a separately built FFmpeg and a fetched video.
- Scope: README reports that all 112 executable files reassemble byte-identically to the Japanese release, that 622k instructions recompile into 22,897 blocks, and that boot, gameplay, audio and bit-exact save states work. The disassembly is code only; graphics, sound and level data stay on the user’s disc. True16:9 widescreen and saves after every zone patch the game’s own programs, so those options depart from the original game.
- Testing evidence: README documents tools/decomp.sh for extracting the disc, reassembling asm/ and comparing each file; tests/rc_check.sh compares per-frame RAM and CPU-PC hashes of recompiled and --interp runs across 96 scripted stages. README also reports SingleStepTests results: all 1.6M Z80 cases, and all 1M 68000 cases apart from some undocumented DIVS/ASR and address-error cases. CI tests only a homebrew test disc.
- License: MIT covers the runtime, tools and installer. third_party/ code, the bundled LGPL 2.1 FFmpeg and LuanUP’s remastered opening, included with permission, keep their own terms, and nothing extracted from a disc is covered. The reviewed LICENSE’s exclusion note names Star Fox 2 rather than Sonic CD. The project is unofficial, unaffiliated with Sega.
About this entry
The description was reviewed against primary sources.
Primary sources
- README.md GitHub · carlosrmz009/littleplanet · Revision 658d834
- LICENSE GitHub · carlosrmz009/littleplanet · Revision 658d834
- tools/decomp.sh GitHub · carlosrmz009/littleplanet · Revision 658d834
- tests/rc_check.sh GitHub · carlosrmz009/littleplanet · Revision 658d834
- .github/workflows/build.yml GitHub · carlosrmz009/littleplanet · Revision 658d834
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