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test(v4.0.0): execute C@ and C! on the golden model

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Both run exactly as written in DECOMPOSITION.md 5.3 and need no change:
four bytes to a cell, little-endian, byte address = 4 * word address +
byte index, at either cell width.

Checked at 32- and 64-bit cells, optimised and ASan+UBSan (`make test`,
`make sanitize`): every byte of two adjacent words, eight values
including ones wider than a byte, with the other bytes of the word, the
upper half of a 64-bit cell and the neighbouring words left untouched.
Breaking C!'s mask or C@'s mask fails.

Headroom (data under args / return): C@ 6/4, C! 5/4.

Test results on the amd64 host only. This is a development check, not
acceptance (JUSTIFICATION.md section 16).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
rajames
2026-10-03 11:16:16 -04:00
co-authored by Claude Opus 5.5
parent f030edcd08
commit 2e4d1330ea
2 changed files with 54 additions and 4 deletions
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docs/v4.0.0/DECOMPOSITION.md
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@@ -330,15 +330,17 @@ Section numbers match the v3 primitive reference.
| `-!` | CAP | `a! NEGATE @ + !` |
| `2@` | CAP | `a! @+ @` (low cell at `addr`, high at `addr+1`, as in v3) |
| `2!` | CAP | `a! SWAP !+ !` |
| `C@` | CAP | See below (D-1). |
| `C!` | CAP | See below (D-1). |
| `C@` | CAP | See below (D-1). Executed on the golden model (2026-10-03). |
| `C!` | CAP | See below (D-1). Executed on the golden model (2026-10-03). |
| `FILL` | CAP | See below. |
| `MOVE` | CAP | `push 2DUP U< IF pop CMOVE> ELSE pop CMOVE THEN` |
| `ERASE` | CAP | `0 FILL` |
| `CELLS` | IN | Empty (word-addressed). Becomes `2* 2*` if D-1 chooses bytes. |
```forth
\ byte access on a word-addressed node, little-endian
\ byte access on a word-addressed node, little-endian: four bytes to a cell at
\ either cell width (so compiled code is the same, D-9), byte address = 4 * word
\ address + byte index. `@` and `!` inside are the opcodes, addressing through A.
: C@ ( baddr -- c )
dup 3 and 3 LSHIFT SWAP 2 RSHIFT a! @ SWAP RSHIFT 255 and ;