Robert Allan JamesandClaude Sonnet 5
70db955ac9
mixed_math_word_m_slash_mod() had the identical bug class already fixed
in M* (commit 9a09949): it reconstructed the dividend from
`(dhigh << 32) | (dlow & 0xFFFFFFFF)`, the same wrong "32-bit halves of a
64-bit value" assumption. Latent for small inputs (fits in 32 bits, so the
reconstruction coincidentally worked), confirmed genuinely broken for a
true wide double -- feeding M*'s own correct 10^24 output into it gave a
quotient/remainder wrong by many orders of magnitude and the wrong sign.
Unlike M*, this one can't just switch to __int128 -- __int128's own `/`/`%`
need libgcc's __udivti3/__umodti3 for 128-bit division, unavailable in
this freestanding, -nostdlib build (the exact constraint
src/starkernel/arch/amd64/timer.c's own doc comment already flagged:
__int128 multiply/shift-by-constant/compare/subtract all compile clean,
only division doesn't). Fixed instead with a hand-rolled unsigned
128-by-64-bit bit-serial (restoring) long division -- 128 iterations of
shift-by-1/compare/subtract only, all in the safe set. Operates on
magnitudes via unsigned negation from 0 (well-defined even for the
extreme negative edge); signs reapplied afterward matching the same C99
truncating-toward-zero convention the previous, narrower implementation
already used, unchanged.
Verified: rebuilt all three architectures, confirmed clean link with no
__udivti3/__umodti3 undefined-symbol errors. Booted and tested all three,
identical results: 1000000000000 1000000000000 M* SWAP 1000000 M/MOD ->
1000000000000000000 remainder 0 (exact division, the case that was wrong
by orders of magnitude before); three sign-combination cases all correct
(-+, +-, --), confirming sign handling survived the magnitude-only
rewrite. T15 (original small-input case) unaffected. Full 24-case
exerciser reran clean on all three, no regressions.
All bugs found by the std79 exerciser campaign, including this one found
while fixing another, are now closed.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EXieurDfDSsDFdnSyusuWo
experiments/
Design of Experiments (DoE) campaign data and analysis for the LithosAnanke kernel.
bare_metal/— the bare-metal DoE experiment: blind full-factorial 2⁴ runs measuring the L8 Jacquard mode selector's effect on the Steady-State Machine across amd64/aarch64/riscv64. Seeexperiments/bare_metal/README.mdfor the full directory layout (runs/,latest/,analysis/{charts,tables,report}).
Hosted-VM DoE campaigns (factorial/heartbeat/ablation studies) live under
docs/working/experiments/ instead — this top-level directory is
specifically the kernel/bare-metal side.