feat(v4.0.0): SM/REM and DNEGATE call-free; execute /MOD and its section 5 words

SM/REM as written in section 4 never returned correctly for a negative
dividend. It holds three entries on the return stack and then calls
DABS -> DNEGATE -> D+ -> U> -> SWAP/U<, which overflows the 9-deep
circular return stack (D-2). DABS itself could not run: DNEGATE as
written (inv SWAP inv SWAP 1 0 D+) left its caller no return entries.

- DNEGATE: inv over if L1 drop push inv 1 + pop ; L1: drop 1 + ;
  i.e. ~d + 1, carrying into the high cell exactly when lo = 0.
- SM/REM: sign tests are native -if (as in 0<) and NEGATE is in line;
  the only calls are DNEGATE and UM/MOD, both call-free inside.

Executed on the golden model at 32- and 64-bit cells, optimised and
under ASan+UBSan:
- SM/REM on dividends built as q*n + r with |r| < |n| and r signed as
  d: every edge-vector q, n with r = 0 and r = +-(|n|-1), plus 20000
  pseudo-random cases.
- /MOD, U>, ABS, S>D, D+ and DABS as written in section 5, against C
  (D+ over all 50625 edge-vector quadruples).
Mutations of DNEGATE's carry and of each SM/REM sign branch are caught.

Headroom (data cells under args / return entries under return address):
  SM/REM 5/3, /MOD 5/2, DNEGATE 7/7, DABS 7/6, ABS 8/7, U> 6/5.
D+ as written is exact but leaves only 1 return entry; recorded in
DECOMPOSITION.md 5.7 as not yet revised.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

This commit is contained in:

rajames

2026-10-02 22:44:04 -04:00

co-authored by

Claude Opus 5.5

parent 3b9d1e4337

commit 93d09840da

2 changed files with 263 additions and 23 deletions

v4/tests/test_foundation.c

+238 -10

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