Olympia G3

G3 is the third-generation Olympia play-by-mail (PBM) strategy game engine (~54K lines of C) — the GitHub-era version with refinements over G2, and the ancestor of the TAG engine.

Sibling engine repositories:

• olympia-g1
• olympia-g2
• olympia-tag

This repository is a standalone extraction of the G3 engine from the original multi-engine Olympia monorepo. It builds on its own with CMake.

The code is legacy K&R-style C originally targeting 32-bit systems. A modernization effort is underway to make it compile cleanly on 64-bit systems.

Important

This is a modernization project, not a development project — no new features. The goal is to bring the existing G3 engine to clean C11 on 64-bit while preserving its exact behavior. Golden output is the contract: every change must keep the golden tests passing (byte-identical), and any behavior change must be deliberate, justified, and re-baselined in the same change (PR). New game features, gameplay tweaks, and scope expansion are out of bounds. See BUILD_HISTORY.md for the full modernization record.

Targets

• olympia-g3 — the main game engine
• mapgen-g3 — the map generator (inputs Map/Land/Cities/Regions, outputs gate/loc/road)
• island-g3 — the island generator

Building

Requires CMake (>= 4.1), Ninja, and a Clang or GCC toolchain.

cmake --preset debug
cmake --build --preset debug
# Binaries: build/debug/{olympia-g3,mapgen-g3,island-g3}

Presets (see CMakePresets.json): debug (default), release, asan-ubsan (AddressSanitizer + UndefinedBehaviorSanitizer on all three targets).

Without presets:

mkdir build && cd build && cmake .. && cmake --build .

32-bit build (Linux, for regenerating golden files)

mkdir build32 && cd build32
cmake -DBUILD_32BIT=ON ..   # requires gcc-multilib
cmake --build .

Running / golden tests

Build first (default debug preset), then:

# mapgen: generates gate/loc/road (inputs to the olympia run below)
./run/mapgen/mapgen.sh

# olympia: extracts fixtures, runs a turn, saves the database
./run/olympia-g3.sh

# compare the olympia run output against the golden snapshot
./tests/olympia/golden_check.sh           # YES = match
./tests/olympia/golden_check.sh --update   # refresh the snapshot

The scripts auto-detect the repo root and look for binaries at build/<preset>/<target> (override the preset with OLYMPIA_PRESET=release ...).

Layout

• olympia/ — the G3 engine sources and headers
• mapgen/ — the map and island generators
• lib/ — shared support code (entity lists, tiles, roads, allocation, …)
• tests/ — golden-test fixtures and golden files
• run/ — run/test driver scripts and scratch run directories
• doc/ — assorted G3 design/reference notes and the modernization playbook
• CLAUDE.md — working guidance (build, test, conventions)
• BUILD_HISTORY.md — full phase-by-phase modernization record
• AUTHORS.md — authors and credits

Authors

See AUTHORS.md. Olympia was created by Rich Skrenta; this repository is maintained and modernized by Michael Henderson.

License

GNU Affero General Public License v3 — see LICENSE. The original Olympia sources are public domain.