carry table

1 files changed, 122 insertions, 22 deletions

diff --git a/Optimizing-assembly-code.md b/Optimizing-assembly-code.md
index 4b191db..dae62eb 100644
--- a/Optimizing-assembly-code.md
+++ b/Optimizing-assembly-code.md
@@ -256,41 +256,84 @@ Or do:
 	xor NCVAL        ; CVAL ^ NCVAL becomes CVAL, 0 becomes NCVAL
 ```
 
-If `NCVAL` is 0 (i.e. set `a` to 0 if not carry), then do:
+And if certain conditions apply, then do something more efficient:
+
+<table>
+
+<tr>
+<th>If this...</th>
+<th>...then do:</th>
+</tr>
+
+<tr><td>
+
+`CVAL` == $FF (aka −1) <br>and<br> `NCVAL` == 0
+
+</td><td>
 
 ```asm
-	; 3 bytes, 3 cycles
-	sbc a    ; if carry, then $ff, else 0
-	and CVAL ; $ff becomes CVAL, 0 stays 0
+	; 1 byte, 1 cycle
+	sbc a ; if carry, then $ff, else 0
 ```
 
-If `CVAL` is 0 (i.e. set `a` to 0 if carry), invert carry and do the same:
+</td></tr>
+<tr><td>
+
+`CVAL` == 0 <br>and<br> `NCVAL` == $FF (aka −1)
+
+</td><td>
 
 ```asm
-	; 4 bytes, 4 cycles
-	ccf       ; invert carry flag
-	sbc a     ; if originally carry, then 0, else $ff
-	and NCVAL ; 0 stays 0, $ff becomes NCVAL
+	; 2 bytes, 2 cycles
+	ccf   ; invert carry flag
+	sbc a ; if originally carry, then 0, else $ff
+```
+
+</td></tr>
+<tr><td>
+
+`CVAL` == 0 <br>and<br> `NCVAL` == 1
+
+</td><td>
+
+```asm
+	; 2 bytes, 2 cycles
+	sbc a ; if carry, then $ff aka -1, else 0
+	inc a ; -1 becomes 0, 0 becomes 1
 ```
 
-If `CVAL` is $FF (i.e. set `a` to $FF if carry), then do:
+</td></tr>
+<tr><td>
+
+`CVAL` == $FF (aka −1)
+
+</td><td>
 
 ```asm
 	; 3 bytes, 3 cycles
 	sbc a     ; if carry, then $ff, else 0
-	or NCVAL  ; $ff stays $ff, $00 becomes NCVAL; omit this if NCVAL is 0
+	or NCVAL  ; $ff stays $ff, $00 becomes NCVAL
 ```
 
-If `NCVAL` is $FF (i.e. set `a` to $FF if not carry), invert carry and do the same:
+</td></tr>
+<tr><td>
+
+`NCVAL` == 0
+
+</td><td>
 
 ```asm
-	; 4 bytes, 4 cycles
-	ccf      ; invert carry flag
-	sbc a    ; if originally carry, then 0, else $ff
-	or CVAL  ; $00 becomes CVAL, $ff stays $ff; omit this if CVAL is 0
+	; 3 bytes, 3 cycles
+	sbc a    ; if carry, then $ff, else 0
+	and CVAL ; $ff becomes CVAL, 0 stays 0
 ```
 
-If `CVAL` equals `NCVAL - 1`, then do:
+</td></tr>
+<tr><td>
+
+`CVAL` == `NCVAL - 1`, <br>aka<br> `CVAL + 1` == `NCVAL`
+
+</td><td>
 
 ```asm
 	; 3 bytes, 3 cycles
@@ -298,7 +341,12 @@ If `CVAL` equals `NCVAL - 1`, then do:
 	add NCVAL ; -1 becomes NCVAL - 1 aka CVAL, 0 becomes NCVAL
 ```
 
-If `CVAL` equals `NCVAL - 2`, then do:
+</td></tr>
+<tr><td>
+
+`CVAL` == `NCVAL - 2`, <br>aka<br> `CVAL + 2` == `NCVAL`
+
+</td><td>
 
 ```asm
 	; 3 bytes, 3 cycles
@@ -306,14 +354,66 @@ If `CVAL` equals `NCVAL - 2`, then do:
 	sbc -NCVAL ; -1 becomes NCVAL - 2 aka CVAL, 0 becomes NCVAL
 ```
 
-If `CVAL` is 0 and `NCVAL` is 1 (i.e. set `a` to 0 if carry, or 1 if not carry), then do:
+</td></tr>
+<tr><td>
+
+`CVAL` == 0
+
+</td><td>
 
 ```asm
-	; 2 bytes, 2 cycles
-	sbc a ; if carry, then $ff aka -1, else 0
-	inc a ; -1 becomes 0, 0 becomes 1
+	; 4 bytes, 4 cycles
+	ccf       ; invert carry flag
+	sbc a     ; if originally carry, then 0, else $ff
+	and NCVAL ; 0 stays 0, $ff becomes NCVAL
 ```
 
+</td></tr>
+<tr><td>
+
+`NCVAL` == $FF (aka −1)
+
+</td><td>
+
+```asm
+	; 4 bytes, 4 cycles
+	ccf     ; invert carry flag
+	sbc a   ; if originally carry, then 0, else $ff
+	or CVAL ; $00 becomes CVAL, $ff stays $ff
+```
+
+</td></tr>
+<tr><td>
+
+`CVAL` == `NCVAL + 1`, <br>aka<br> `CVAL - 1` == `NCVAL`
+
+</td><td>
+
+```asm
+	; 4 bytes, 4 cycles
+	ccf      ; invert carry flag
+	sbc a    ; if originally carry, then 0, else $ff aka -1
+	add CVAL ; -1 becomes CVAL - 1 aka NCVAL, 0 becomes CVAL
+```
+
+</td></tr>
+<tr><td>
+
+`CVAL` == `NCVAL + 2`, <br>aka<br> `CVAL - 2` == `NCVAL`
+
+</td><td>
+
+```asm
+	; 4 bytes, 4 cycles
+	ccf       ; invert carry flag
+	sbc a     ; if carry, then 0, else $ff aka -1; doesn't change the carry flag
+	sbc -CVAL ; -1 becomes CVAL - 2 aka NCVAL, 0 becomes CVAL
+```
+
+</td></tr>
+
+</table>
+
 
 ### Increment or decrement `a` when the carry flag is set