2EZDecomp

Matching decompilation of a 2000s arcade rhythm game (no game content included)

Written in	C++
License	GPL-3.0
Last updated	10 Oct 2026

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A matching decompilation of a 2000s PC-based arcade rhythm game: C/C++ source reconstructed so that, built with the original toolchain (Microsoft Visual C++ 7.1, cl.exe 13.10.3077), each function compiles to the same bytes as the original executable. Progress is checked function by function with reccmp.

This repository contains no game content. There is no executable, no assets, no music or charts, no key or data tables, and no hexdumps. Building or verifying anything requires your own legally obtained copy of the game. The project is not affiliated with, endorsed by, or connected to the game's developers or rights holders. Any product names that appear in the source or docs refer to the original software and are the property of their owners.

Target

The matching target is one specific build. Identify yours before building:


Version	2.05: shown as "Version 2.05" on the test-mode screens (the build number `205` at `0x4a8d6c`)
Build date	2021-07-30 (PE timestamp)
Data version	`GameVersion = 150` in `system/title/Common/version.ini` (written to the log as "Game Version = 150")
Executable SHA-256	`858ca451ca16225ce56d7b902c61f2c7bb813d8c65b85131d85e77fb566af833` (as shipped, `EZ2AC.exe`)
Matching image SHA-256	`e7d85105b417add292efdc3116e7d2cf73301588f2741dddef93bed107a9ded8` (`original/EZ2AC_Unpacked.exe`, the unpacked image reccmp compares against; also in `reccmp-project.yml`)

The shipped executable is packed. The unpacked image must be produced from your own copy; this repository does not include one or describe how.

Progress

Every function in the game has decompiled C. The map shows how much of it already compiles to exactly the original bytes: each cell is 64 bytes of the original code, in address order, coloured by its function's match.


Functions decompiled	1474 / 1474 (100%)
Functions byte-identical	1300 / 1474 (88.2%)
Code byte-identical	62.5% (309,969 of 495,930 bytes)
Average similarity (reccmp)	97.6%

The byte share trails the function count because the largest functions (screen directors, the game loop) are the hardest to match. Figures are regenerated with scratchpad/progress.py (see CONTRIBUTING.md).

Contributing

See CONTRIBUTING.md: how to pick a target, read a diff, use the codegen cookbook and the source permuter, and check that a change keeps the behaviour.

Layout

Path	What it is
`src/`, `include/`	the reconstructed source (one `// FUNCTION:` annotation per original address)
`match.sh`	build with the VC7.1 toolchain under Wine and run reccmp
`docs/cookbook.md`	every codegen pattern learned while matching, with evidence
`scratchpad/`	analysis and verification scripts (see `scratchpad/perm/README.md` for the source permuter)
`scratchpad/fmt/`	runs the decomp's own file-format code on the user's game data and diffs it against an independent decoder
`reccmp-patches/`	patches to reccmp used by this project (AGPL-3.0, see that folder)
`wip/`	analysis notes
`docs/progress/`	the progress map, badges and figures (`scratchpad/progress.py`)
`CLAUDE.md`	the working rules and conventions of the project

Building and matching

You need, none of which is included:

Microsoft Visual C++ .NET 2003 (cl.exe 13.10.3077, link.exe 7.10), the Windows Server 2003 SP1 Platform SDK and the DirectX 8 SDK, under tools/;
Wine, with a dedicated prefix in tools/wineprefix (see CLAUDE.md for the settings that keep the build headless);
reccmp (with the patches in reccmp-patches/) in .venv;
your own copy of the game's executable in original/.

Then ./match.sh builds everything and prints the match table, and ./match.sh 0xADDRESS shows the diff for one function.

Licence

The reconstructed source, scripts and documentation are released under the GNU General Public License v3.0 or later (LICENSE). The files in reccmp-patches/ modify reccmp and are under the GNU Affero General Public License v3.0 or later, as reccmp is. This licence covers only the contributors' own work; it grants nothing in the original game.

This page is synced from README.md in the 2EZDecomp repo.