849c5069fc
Seven End Turns from ref-turn2.sav on VM140, six control words, whole-state checksum on every post-turn autosave. 53-bit and 64-bit x87 give byte-identical state across all 35,394 leaves, so an x64/SSE port computing in IEEE double has NO double-rounding budget to preserve and floats=bits is free. Two settings do move state, each reproduced on a repeat run: 0x007f (24-bit) Sys[112 "Gamma Cephei"]/Pop2/PopG/PopC 540000000 -> 540000002 0x1a7f (round-up) Flt[34 "Beta Fleet"]/Pos/.[0] and /Pos/.[2], 1 ULP each So the port must hold intermediates at 53 bits and use round-to-nearest -- both SSE defaults, now measured rather than assumed, each with a named regression witness. The briefed triple was under-powered: 0x027f is 53-bit (it differs from 0x127f only in bit 12, infinity control, ignored since the 387) and 0x137f is 64-bit, not a rounding change. Run as written all three come back identical, and that would have "proved" something false on both axes that matter. Evidence the forced word actually held: read-back at each force site plus 38 independent in-pipeline hook samples per run spanning turn phases 4, 6 and 8, all reading the forced value. Mars::Application::Run calls _controlfp(0x50000,0x3070300) at 0x0089f606 every frame, which is 0x127f, so forcing at StrategyClient::EndTurn is wiped before the turn runs; StrategyServer::BeginProcessTurn is the point that works. Also re-confirms the End-Turn determinism oracle on engine cef889e: bb4fd9ac... / 978041ac... unchanged. New tools: verify/fpu-cw/cw_census.py, verify/fpu-cw/trace_bitdiff.py (the latter exists because under a forced 24-bit word the CRT's own %g rendering degrades, so trace text is not a valid comparison surface).
72 lines
2.5 KiB
Python
72 lines
2.5 KiB
Python
#!/usr/bin/env python3
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"""Census of the `fpu_cw` field the shim's template hooks record on every call.
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Each hook snapshots the x87 control word as it finds it, so a run's trace carries independent
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samples of the word from *inside* the turn pipeline -- phase 4 (MoveFleet), phase 6
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(ServerSystem::ProcessTurn) and phase 8 (ComputeBudget / ProcessResearch). That is the evidence
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that a control word forced at the turn gate actually held for the duration of the turn, rather
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than being silently restored partway through (which would produce identical saves and a
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completely false "nothing depends on precision" conclusion).
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Usage: cw_census.py <shim.trace.jsonl> [...]
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"""
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import gzip
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import json
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import sys
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from collections import Counter, defaultdict
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def _open(path):
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op = gzip.open if path.endswith(".gz") else open
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return op(path, "rt", encoding="utf-8", errors="replace")
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def census(path):
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per_hook = defaultdict(Counter)
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first_last = {}
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n = 0
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with _open(path) as f:
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for line in f:
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line = line.strip()
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if not line.startswith("{"):
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continue
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try:
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rec = json.loads(line)
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except json.JSONDecodeError:
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continue
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hook = rec.get("hook")
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if not hook:
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continue
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n += 1
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for arg in rec.get("args", []) or []:
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if arg.get("n") == "fpu_cw":
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cw = int(arg["v"])
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per_hook[hook][cw] += 1
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key = (hook, cw)
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if key not in first_last:
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first_last[key] = [rec.get("call_id"), rec.get("call_id")]
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else:
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first_last[key][1] = rec.get("call_id")
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return n, per_hook, first_last
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def main():
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for path in sys.argv[1:]:
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n, per_hook, first_last = census(path)
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print(f"== {path} ({n} hook records)")
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total = Counter()
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for hook in sorted(per_hook):
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for cw, count in sorted(per_hook[hook].items()):
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lo, hi = first_last[(hook, cw)]
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total[cw] += count
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print(f" {hook:<42} cw=0x{cw:04x} x{count:<5} call_id {lo}..{hi}")
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if not per_hook:
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print(" (no hook recorded an fpu_cw field)")
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else:
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vals = ", ".join(f"0x{cw:04x} x{c}" for cw, c in sorted(total.items()))
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print(f" ALL SAMPLES: {vals}")
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print()
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if __name__ == "__main__":
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main()
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