# CodeGen (`codegen.txt` 1746 lines, `CODEGEN.DEF/MOD`)

MCode emitter with peephole folding + 2KB sliding window on the output
file (`Scanner.global4`) + fixup queue for jumps.

Opcodes: see `CODEGEN.MOD` const block (`OPLLD=08H ... OPCALL=0EDH ...`),
consumed by `MCode_specification/*.mod`.

## State

| old | proposed |
|---|---|
| global2/3/4 | `nextEmit/winBase/winLimit` (init 16/0/4096) |
| global5 | `emitEnabled` |
| global6 | `window[0..2047]` (`= ADR(Scanner.global21)`) |
| global7/8/9/10 | `pendMode/pendSize/pendDisp/pendOff` |
| global11/12 | `fixQueue[0..15]/fixCount` (`{kind,word1/word2\|ptr\|long}`) |
| global14/15 | `pendFlag/checkOverflow` (`execute=4`) |

## Procedures (proposed)

| old | proposed |
|---|---|
| Emit1/Emit2/EmitWord/EmitString | same (guard `OverflowGuard`, flush if full) |
| proc19/20 | `PeekByte/PokeByte` (window or `SetPos+Read/WriteByte`) |
| proc23 | `FlushWindow` (write 2048, slide tail) |
| proc28 | `SeekWindow` (512-align, refill) |
| proc29 | `OverflowGuard` (`nextEmit >= ComLine.codepos -> RAISE 281`) |
| proc26 | `Assert` |
| proc22/24 | `OpenEmit/InitCode` |
| proc4 | `DiscardPend` |
| proc5/30/31/32 | `SetPend/FlushPendOp/BaseOp/FlushQueue` (peephole: `LDIX/LONGREAL/LI/LB...`) |
| proc8/9 | `QueueConst/QueueLong` |
| proc6 | `EmitOp(sub,type)` (fold `NEG/power2/AND/EQ0`, types 0..5: long/short/DCOMP/REALCMP/set/extern) |
| proc7 | `EmitExt` |
| proc10 | `EmitStd` (`LIMIT` fold) |
| proc11 | `EmitMisc` |
| proc17/18 | `EmitSys/EmitExt3` |
| proc12/13/14/15/16 | `OpenFix/CloseFix/InsertFix/AdjustFix/MarkFix` (short `224`-case vs word fixups) |