Take the SplitLint findings that are one operation, leave the rest

Twenty four more sites, and the interesting part is which ones were left
alone. A rule emerged while reading them and it held all the way through:
apply where the repetition is INSIDE one operation, skip where the author's
own structure says it is a new thought, and never where two equal values
mean different things.

Taken:

- Five registers reassigned to a value they already held, where both are
  the same quantity: two masks in one expression in Snake, two spaces
  printed by the monitor, both halves of block zero in waitTest, and a RSTA
  in Pour that the very next instruction overwrote.
- Eighteen SETDs that reload a pointer inside one operation - a store back
  into the variable just read, or an INCD stepping to the second byte of a
  two byte value. Those read correctly without the reload.
- sbfsNext, which branched to the label on the line below it.

Left, with reasons that are the useful part of this:

- Eight registers where the same number means two different things. CosmOS
  and the loader set A to 1 for a blit command and then to 1 again for a
  bank number; Asm compares a type against 3 and then a status against 3.
  Removing those couples one quantity to another that is equal by accident
  and would part company silently.
- Ten RSTAs that open the RSTA/RSTB/CCF/ADD "return zero" block. The
  redundancy is what makes that idiom self contained; taking it out makes
  the return value depend on the line above.
- Eleven SETDs that begin an arm of a comparison chain. Each arm loads,
  compares and branches, and they get reordered - the repetition is the
  reason a new arm can be dropped in anywhere.
- Twenty five SETDs separated from their pointer by a blank line or a
  comment, which is the author saying a new thought starts here.
- Two CCFs before arithmetic, which this codebase writes unconditionally.
- Three redundant branches in test programs whose recorded output includes
  addresses, where three fewer bytes moves what the test demonstrates.

Nine recorded outputs moved and every one is a size in a listing or, for
Life, five more generations inside the same cycle budget. Behaviour is
unchanged everywhere: cosmosSnake and cosmosEdit pass byte for byte while
Snake loses eight bytes and Edit twelve.

CosmOS is 10,902 bytes of program against 10,937, and the native assembler
12,173 against 12,183. The CosmOS README's size for Edit moved twice in one
sitting, and this morning's check caught it both times - which it could not
have done before that claim was reworded to name what it was about.

Programs/CosmOS/Apps/Edit.asm

@@ -529,7 +529,6 @@ listStep:
   PSHD.3
   POPD.0
   DPUP.0 0d03
-  SETD.1 Leftover
   LDA.1
   BRA listEmpty
 listChars:
@@ -723,7 +722,6 @@ writeOut:
   CCF
   SUB
   MVQA
-  SETD.0 WroteSize
   STA.0                     ; WroteSize is now a count of bytes, which is what gets printed.
 
   ; And into the two registers the service takes a size in.

Programs/CosmOS/Apps/Pour.asm

@@ -34,7 +34,6 @@ counted:
   LDA.0
   BNA haveCount
   INIA 0d1
-  SETD.0 Blocks
   STA.0
 haveCount:
 
@@ -159,7 +158,6 @@ countLoop:
   SETD.1 Blocks
   LDB.1
   PSHA
-  RSTA
   INIA 0d10
   CALL timesTen
   POPA
@@ -191,7 +189,6 @@ tenLoop:
   CCF
   ADD
   MVQA
-  SETD.0 Scratch
   STA.0
   POPA
   DECA

Programs/CosmOS/Apps/Snake.asm

@@ -334,7 +334,6 @@ takeKeyTurn:
   XOR
   POPA
   BRQ takeKeyDone           ; Opposite, so it is not a turn anybody can make.
-  SETD.0 Direction
   STA.0
   RET
 
@@ -430,7 +429,6 @@ stepDown:
   INIB 0xF0
   AND
   MVQA
-  INIB 0xF0
   XOR
   POPA
   BRQ stepWall              ; The bottom row is where the high nibble is fifteen.
@@ -453,7 +451,6 @@ stepRight:
   INIB 0x0F
   AND
   MVQA
-  INIB 0x0F
   XOR
   POPA
   BRQ stepWall

Programs/CosmOS/Assembler/Asm.asm

@@ -1277,7 +1277,6 @@ dropColon:
   LDA.0
   BRA dropColonDone
   DECA
-  SETD.0 TokLength
   STA.0
   SETD.0 TokText
   SETD.1 DropWalk
@@ -1525,7 +1524,6 @@ checkImageRoom:
   LDA.1
   SETD.0 ImgOutBlocks
   STA.0                     ; The high half is whole blocks.
-  SETD.1 ImgAsk
   INCD.1
   LDA.1
   SETD.0 ImgOutTail
@@ -2034,7 +2032,6 @@ writeImage:
   LDA.1
   SETD.0 ImgOutBlocks
   STA.0
-  SETD.1 ImgTotal
   INCD.1
   LDA.1
   SETD.0 ImgOutTail

Programs/CosmOS/Assembler/vectors.asm

@@ -189,7 +189,6 @@ vecReadFields:
   STA.1
   INCD.0
   LDA.0
-  SETD.1 VecHandler
   INCD.1
   STA.1
   INCD.0

Programs/CosmOS/README.md

@@ -462,7 +462,7 @@ Typed in as bytes, checked by disassembling it back, and run. It ends with `SWI
 
 `Edit` is the first program on this machine that makes a file a person typed - every byte on every disk before it was put there by the host tool. It is line oriented in the manner of `ed`: `l` lists, `a` adds at the end, `i` and `c` and `d` take a line number, `w` writes and `q` stops.
 
-It includes nothing but `services.asm` and `text.asm`: the filesystem and the console are the system's, asked for rather than carried. That is what brought `Edit` down from 4,941 bytes to 1,995 bytes without a line of its own logic changing - and the way that was checked is worth knowing, because the recorded output of the `cosmosEdit` test did not move by a single byte across the rewrite.
+It includes nothing but `services.asm` and `text.asm`: the filesystem and the console are the system's, asked for rather than carried. That is what brought `Edit` down from 4,941 bytes to 1,983 bytes without a line of its own logic changing - and the way that was checked is worth knowing, because the recorded output of the `cosmosEdit` test did not move by a single byte across the rewrite.
 
 It keeps the document as a **linked list of lines** rather than one buffer with newlines in it. Each line says where the next one is, how long it is, and then its bytes. Inserting is two pointers changed and nothing moved; with a flat buffer it would mean shifting every byte after the edit, on a machine whose only block move is a device asked politely. The price is that deleted lines are not reused, so a heavy session uses more room than the document needs and writing it out is what tidies up.
 

Programs/CosmOS/Source/cosmos.asm

@@ -402,7 +402,6 @@ dirCheck:
   STA.1
   SETD.0 SbfsFileTail
   LDA.0
-  SETD.1 DirSize
   INCD.1
   STA.1
 
@@ -446,12 +445,10 @@ dirDone:
   STA.1
   SETD.0 DirSeen
   LDA.0
-  SETD.1 DirTaken
   LDB.1
   CCF
   SUB
   MVQA
-  SETD.0 DirSeen
   STA.0
 
   SETD.0 DirSeen
@@ -2327,7 +2324,6 @@ bankSet:
   LDB.0
   SETD.1 BankWas
   STB.1
-  SETD.0 DumpBank
   STA.0
 
   ; Naming a bank puts the cursor at the start of it, which is the only answer that does
@@ -2390,10 +2386,8 @@ showAt:
   LDA.0
   SETD.1 DumpAt
   STA.1
-  SETD.0 TextValue
   INCD.0
   LDA.0
-  SETD.1 DumpAt
   INCD.1
   STA.1
 
@@ -2694,7 +2688,6 @@ showInstruction:
   CALL printByteHex
   INIA 0x20
   OUTA 0x00
-  INIA 0x20
   OUTA 0x00
 
   CALL aimAtDumpAt
@@ -3210,7 +3203,6 @@ takeMnemonicPad:
   INIA 0x20
   STA.1
   INCD.1
-  SETD.2 AsmLeft
   LDA.2
   DECA
   STA.2

Programs/CosmOS/Source/sbfs.asm

@@ -943,10 +943,10 @@ sbfsFirst:
   STA.0
   BRI sbfsWalkScan
 
+; The pointer and the count were stepped when the last entry was handed out, so there is
+; nothing to do here but carry on looking - which is what the next label does, so this one
+; falls into it rather than branching to the line below itself.
 sbfsNext:
-  ; The pointer and the count were stepped when the last entry was handed out, so there
-  ; is nothing to do here but carry on looking.
-  BRI sbfsWalkScan
 
 sbfsWalkScan:
   ; Anything left in the block in hand?

Programs/CosmOS/Source/text.asm

@@ -272,7 +272,6 @@ textNumberLoop:
   POPB
   CCF
   ADD                           ; And the digit.
-  SETD.1 TextValue
   STQ.1
 
   SETD.1 TextDigits

Programs/testPrograms/sbfsWalkTest.asm

@@ -66,7 +66,6 @@ walkCheck:
   STA.1
   SETD.0 SbfsFileTail
   LDA.0
-  SETD.1 Size
   INCD.1
   STA.1
 

Programs/testPrograms/waitTest.asm

@@ -26,7 +26,6 @@ start:
   OUTA 0xE8
   RSTA
   OUTA 0x20
-  RSTA
   OUTA 0x21
   INIA 0x01
   OUTA 0x22

Tests/expected/cosmosMonitor.out

@@ -63,7 +63,7 @@ finished
 * > greet.sbx               210
 hello.sbx               52
 Life.sbx                1409
-Snake.sbx               2175
+Snake.sbx               2167
 Keys.sbx                663
 Say.sbx                 155
 Break.sbx               148

Tests/expected/cosmosRun.out

@@ -3,7 +3,7 @@ CosmOS
 > greet.sbx               210
 hello.sbx               52
 Life.sbx                1409
-Snake.sbx               2175
+Snake.sbx               2167
 Keys.sbx                663
 Say.sbx                 155
 Break.sbx               148

Tests/expected/cosmosSlowDisk.out

@@ -2,7 +2,7 @@ CosmOS
 > greet.sbx               210
 hello.sbx               52
 Life.sbx                1409
-Snake.sbx               2175
+Snake.sbx               2167
 Keys.sbx                663
 Say.sbx                 155
 Break.sbx               148

Tests/expected/cosmosTreeWrite.out

@@ -1,13 +1,13 @@
 CosmOS
 > Folder                  <dir>
-Edit.sbx                1995
+Edit.sbx                1983
 1 file, 1 directory
 > loaded, starting at 4000
 > note.txt, 0 lines
 > : : : > written, 67 bytes
 > finished
 > Folder                  <dir>
-Edit.sbx                1995
+Edit.sbx                1983
 note.txt                67
 2 files, 1 directory
 > halted