Fix SWAP-MTX: Fisher-Yates shuffle was never actually shuffling correctly

Found while building the analysis report for the ACL-RWT relaunch
campaign: cfg=0 was missing from run coverage for 2 of 3 seeds, reproduced
identically across all three architectures. Root-caused rather than
worked around, per Captain Bob's "this is worrisome."

SWAP-MTX (capsules/doe.4th Block 2104) never actually swapped two
RUN-MATRIX cells -- it performed a lossy one-way copy (second MATRIX!
call mis-targeted mat[i] again instead of mat[j]). Confirmed by direct
empirical test on the hosted build: INIT-MATRIX gives mat[0]=0, mat[5]=5;
after 0 5 SWAP-MTX, mat[0]=0 (unchanged, should be 5) and mat[5]=0
(correct), with the original value 5 permanently destroyed. Every
Fisher-Yates shuffle this mechanism has ever run silently duplicated some
values and dropped others -- not a true permutation. Not new, not
introduced by item 4.6/Stadium work; predates this session.

Fixed with explicit temp variables (SW-I/SW-J/SW-VI/SW-VJ), trivially
verifiable by inspection over clever stack juggling. Verified on the
hosted build for all three seeds used by the relaunch campaign: each now
produces all 16 cfg values exactly 30 times, run_id 0-479 fully distinct.
Three-arch QEMU acceptance clean: 1012/0/0 POST on all three, identical
dict_hash (expected -- doe.4th isn't C-registered or auto-loaded at
boot). BLOCK_MAP.md correctly shows only doe.4th's own hash changed.

Also includes the R analysis/chart pipeline (analyse_stadium_relaunch.R)
built for the relaunch campaign report, and the three acceptance boot
logs.

Retroactive caveat: the relaunch campaign's own run-matrix coverage
(experiments/bare_metal/runs/acl-rwt-20260820/) is not a valid uniform
permutation, having run against the buggy shuffle. Whether to re-run it
against the fix is a separate call, not made here.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

This commit is contained in:

Robert Allan James

2026-08-20 10:56:12 -04:00

co-authored by

Claude Sonnet 5

parent 79d160c1ca

commit 7e2fd9f044

23 changed files with 44760 additions and 13 deletions

lfs/amd64/starforth

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