Executed on the golden model as written, and correct: <, =, D<, 2OVER,
and Q.=, Q.<, Q.0= (the D=, D<, D0= words).
Fixed, because they could not work under D-2 or were wrong:
- DMAX, DMIN: 2OVER 2OVER D< needs 8 data cells plus D<'s 2, the whole
10-deep data stack, so both failed on every case once the caller held
anything. Rewritten on a new call-free helper
(D<) ( d1 d2 -- d1 d2 flag )
which compares copies of the high cells, then the low cells unsigned
on a tie, with in-line sign tests; DMAX and DMIN then drop the loser.
- 2SWAP: ROT and SWAP written in line. Return headroom 2 -> 4, which
also lifts 2OVER 1 -> 3 and Q.> 1 -> 2.
- Q.>: section 5.26 gave SWAP D<, which swaps single cells; it was wrong
in 11702 of 20169 cases. Now 2SWAP D<.
Checked at 32- and 64-bit cells, optimised and ASan+UBSan: every
edge-vector quadruple (50625) for D<, (D<), 2SWAP, 2OVER, DMAX and DMIN;
Q comparisons on every pair of 13 edge Q values plus 20000 pseudo-random
pairs weighted to ties and one-bit differences, signed (D-8) and against
v3's unsigned comparisons where both values have the same sign.
Mutating any (D<) branch or subtraction fails 700+ checks.
The new fatal-UBSan setting caught a test-side array overflow in the
headroom probe (results buffer sized 4, six needed); fixed.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
