d462513f84
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.
31 lines
1.6 KiB
Text
31 lines
1.6 KiB
Text
# Lane F, x87 precision-sensitivity experiment (verify/results/fpu-cw in the notes repo).
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# 0x127f = 53-bit significand, round-to-nearest. THE CONTROL: exactly what the game sets itself, so this run must reproduce the stock oracle hashes.
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#
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# Every shim.cfg.fpu* file is identical except the fpu.force line: the hook set, the trace path
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# and the flush policy are held fixed so the control word is the only variable across runs.
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#
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# x87 control-word fields: bits 0-5 exception masks, bits 8-9 precision control
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# (00 = 24-bit / 10 = 53-bit / 11 = 64-bit significand), bits 10-11 rounding control
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# (00 nearest / 01 down / 10 up / 11 truncate), bit 12 infinity control (ignored since the 387).
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hooks=trace
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hook.Shim::SelfTest::Fill=off
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hook.Mars::GlobalConsts::LoadFile=off
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hook.Game::WeaponDictionary::Init=off
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hook.Game::SectionDictionary::SectionDictionary=off
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hook.Game::StrategyServer::ProcessFleetMovement=off
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hook.Game::TechTree::ProcessResearch=trace
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hook.Game::ServerPlayer::ComputeBudget=trace
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hook.Game::ServerPlayer::OnTechResearched=trace
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hook.Game::ServerSystem::ProcessTurn=trace
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hook.Game::StrategyServer::MoveFleet=trace
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trace.path=C:\SOTS\shim.trace.jsonl
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trace.inline_max=256
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trace.flush=always
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# Forced once at the turn gate (StrategyClient::EndTurn and StrategyServer::BeginProcessTurn),
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# never re-forced inside the pipeline -- re-forcing would guarantee the value is present without
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# proving it ever held.
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fpu.force=0x127f
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# Per-tick sampler: logs to shim.log whenever the word MOVES, so the log carries a timeline of
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# the value rather than a single claim made at a single instant.
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fpu.sample_ticks=on
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