From-scratch reimplementation of the Sword of the Stars (2006) engine. Clean-room; engine code only — bring your own game copy. Planning/RE evidence live in sots-re.
Find a file
alex d462513f84 shim: force and verify the x87 control word around the turn gate
New fpu_force module (4 register-transparent asm stubs, same pattern as the M0
Initialize hook, so the [unverified] prototypes of the turn-gate functions are
never relied on) plus two shim.cfg keys:

  fpu.force=<cw>|off      fldcw at StrategyClient::EndTurn and
                          StrategyServer::BeginProcessTurn, and nowhere else
  fpu.sample_ticks=on|off per-frame sampler, logs only when the word CHANGES

Forcing is deliberately one write per turn: re-forcing inside the pipeline would
guarantee the value is present without proving it ever held, which is the exact
false negative this experiment has to avoid. Verification is kept separate --
StrategyServer::ProcessTurn is hooked sample-only, and its reading plus the
existing per-hook fpu_cw fields (38 samples per turn across phases 4, 6 and 8)
are what establish that the setting lasted the whole turn.

Six shim.cfg variants, identical apart from the fpu.force line, and docs.

Used to settle STATE_CHECKSUM.md 3.5: 53-bit and 64-bit x87 produce byte-
identical turn results, so an x64/SSE port has no double-rounding budget to
preserve; 24-bit and round-up each move exactly one thing. Findings and evidence
live in the notes repo (findings/subsystems/fpu-precision-sensitivity.md).

clean_room_check.sh OK; host ctest 32/32.
2026-09-08 05:09:16 -04:00
cmake m0: binkw32 proxy shim, minhook, trace hook on Application::Initialize; build/deploy tooling 2026-09-07 17:22:15 -04:00
docs shim: force and verify the x87 control word around the turn gate 2026-09-08 05:09:16 -04:00
include/generated sync generated header (386 entries) after movefleet merge 2026-09-08 03:53:49 -04:00
src shim: force and verify the x87 control word around the turn gate 2026-09-08 05:09:16 -04:00
tests movefleet: reproduce the original's float32 normalise; 8 of 45 live divergences -> 0 2026-09-08 03:50:04 -04:00
third_party mars/vfs: gob ZIP reader + native override, miniz 3.1.2; oracle-verified 8352+2035 entries 2026-09-07 17:40:51 -04:00
tools b4: colony + movement hooks; 22 formula corrections (growth curve has no capacity term, range margin +0.05f, ties-to-even rounding); 3 verified signatures 2026-09-08 00:57:55 -04:00
.gitignore init commit 2026-09-07 17:07:54 -04:00
CMakeLists.txt shim: force and verify the x87 control word around the turn gate 2026-09-08 05:09:16 -04:00
CMakePresets.json m0: binkw32 proxy shim, minhook, trace hook on Application::Initialize; build/deploy tooling 2026-09-07 17:22:15 -04:00
CONTRIBUTING.md init commit 2026-09-07 17:07:54 -04:00
LICENSE init commit 2026-09-07 17:07:54 -04:00
README.md b3: research hook + RNG-snapshot compare design; fix draw mapping to y/(2^32-1), NextInt inclusive, float32 odds, spend floor, decay constants 2026-09-07 23:14:08 -04:00

sots-engine

A from-scratch, functional reimplementation of the engine behind Sword of the Stars (2006). Not a byte-for-byte decompilation: behavior-equivalent code, built up one verified piece at a time (OpenRCT2-style) until the tree can build the whole application on its own.

Bring your own game. This repository contains engine code only. Game data, assets, saves, and the original binaries are never included; tests and tools read an owner-supplied copy via $SOTS_DATA_DIR. See CONTRIBUTING.md for the clean-room rules.

Status

Phase 2. M0 done — the shim frontend (src/shim/, a proxy binkw32.dll the original game loads) builds, deploys, hooks, and logs from a real game launch. Engine code accrues under src/mars/ and src/game/; each module is oracle-verified against the owner's game data before merge:

  • mars/parse — brace-block + .effect readers (1,531/1,531 files agree with the reference)
  • mars/text — flat key/value tables, id manifests, CSV (64/64 files agree)
  • game/sim — strategic formulas (economy, research, colonies, movement) as pure functions; 356 hand-computed checks
  • mars/vfs — .gob (ZIP) archive reader + loose-file override; entry counts and bytes verified against unzip
  • mars/stream — the game's self-describing save/serialization format (reader, writer, typed shapes) + gzip; three real saves round-trip byte-identical
  • mars/rng — MT19937 with save-state load/store; layout confirmed against real saves, draw mappings read off the binary (docs/mars-rng.md)
  • game/data — typed catalogs (weapons, ship sections, turrets, id registries, tech tree, strings) with cross-reference checks; 229k values agree with the reference
  • game/design — ship-design assembly/fit/tech-gating rules and derived stats; validates all 127 stock designs from real saves

Build: cmake --preset host && cmake --build --preset host && ctest --preset host (Linux); tools/sync-build.sh cross-builds the shim on the lab box and stages it for deployment.

Layout (grows with the work)

  • src/shim/ — binkw32 proxy + hooks + old-vs-new compare harness (frontend #1)
  • src/mars/, src/game/ — the engine and game reimplementation (accruing)
  • include/generated/sots_addresses.h — binary facts (RVAs/prototypes), generated from the RE repo
  • tests/ — host tests; real-data tests skip unless $SOTS_DATA_DIR is set
  • tools/ — build (MinGW i686 cross) and deploy scripts

Planning, findings, and verification evidence are tracked in the private RE repo (sots-re).