forth: double-cell ops D+/D-/DNEGATE/DABS/D=/D</D0=/D0</DMAX/DMIN (+18)

plans/forth-on-sx.md

@@ -88,7 +88,7 @@ Representation:
 - [x] Memory: `CREATE`, `HERE`, `ALLOT`, `,`, `C,`, `CELL+`, `CELLS`, `ALIGN`, `ALIGNED`, `2!`, `2@`
 - [x] Unsigned compare: `U<`, `U>`
 - [x] Mixed/double-cell math: `S>D`, `M*`, `UM*`, `UM/MOD`, `FM/MOD`, `SM/REM`, `*/`, `*/MOD`
-- [ ] Double-cell ops: `D+`, `D-`, `D=`, `D<`, `D0=`, `2DUP`, `2DROP`, `2OVER`, `2SWAP` (already), plus `D>S`, `DABS`, `DNEGATE`
+- [x] Double-cell ops: `D+`, `D-`, `D=`, `D<`, `D0=`, `2DUP`, `2DROP`, `2OVER`, `2SWAP` (already), plus `D>S`, `DABS`, `DNEGATE`
 - [ ] Number formatting: `<#`, `#`, `#S`, `#>`, `HOLD`, `SIGN`, `.R`, `U.`, `U.R`
 - [ ] Parsing/dictionary: `WORD`, `FIND`, `EXECUTE`, `'`, `[']`, `LITERAL`, `POSTPONE`, `>BODY`, `DOES>`
 - [ ] Source/state: `SOURCE`, `>IN`, `EVALUATE`, `STATE`, `[`, `]`
@@ -106,6 +106,15 @@ Representation:
 
 _Newest first._
 
+- **Phase 5 — double-cell ops `D+`/`D-`/`DNEGATE`/`DABS`/`D=`/`D<`/`D0=`/
+  `D0<`/`DMAX`/`DMIN` (+18; Hayes unchanged).** Doubles get rebuilt
+  from `(lo, hi)` cells via `forth-double-from-cells-s`, the op runs
+  in bignum, and we push back via `forth-double-push-s`. Hayes Core
+  doesn't exercise D-words (those live in Gerry Jackson's separate
+  `doublest.fth` Double word-set tests we have not vendored), so the
+  scoreboard stays at 446/638 — but the words now exist for any
+  consumer that needs them.
+
 - **Phase 5 — mixed/double-cell math; Hayes 342→446 (69%).** Added
   `S>D`, `D>S`, `M*`, `UM*`, `UM/MOD`, `FM/MOD`, `SM/REM`, `*/`, `*/MOD`.
   Doubles ride on the stack as `(lo, hi)` with `hi` on top.