More

1 files changed, 48 insertions, 26 deletions

diff --git a/Optimizing-assembly-code.md b/Optimizing-assembly-code.md
index dd46669..d9b3811 100644
--- a/Optimizing-assembly-code.md
+++ b/Optimizing-assembly-code.md
@@ -99,7 +99,7 @@ Don't do:
 ```asm
 	; 4 bytes, 4 cycles
 	ld b, a
-	ld a, CONST
+	ld a, FOOBAR
 	sub b
 ```
 
@@ -108,21 +108,23 @@ But do:
 ```asm
 	; 3 bytes, 3 cycles
 	cpl
-	add CONST + 1
+	add FOOBAR + 1
 ```
 
+("What's [foobar](https://en.wikipedia.org/wiki/Foobar)?")
+
 
 ### Set `a` to one constant or another depending on the carry flag
 
-(The example sets `a` to `ONE` if the carry flag is set (`c`), or `TWO` is the carry flag is not set (`nc`).)
+(The example sets `a` to `FOO` if the carry flag is set (`c`), or `BAR` is the carry flag is not set (`nc`).)
 
 Don't do:
 
 ```asm
 	; 6 bytes, 6 or 7 cycles
-	ld a, ONE
+	ld a, FOO
 	jr c, .carry
-	ld a, TWO
+	ld a, BAR
 .carry
 ```
 
@@ -130,9 +132,9 @@ And don't do:
 
 ```asm
 	; 6 bytes, 6 or 7 cycles
-	ld a, TWO
+	ld a, BAR
 	jr nc, .no_carry
-	ld a, ONE
+	ld a, FOO
 .no_carry
 ```
 
@@ -141,8 +143,8 @@ But do:
 ```asm
 	; 5 bytes, 5 cycles
 	sbc a         ; if carry, then $ff, else 0
-	and ONE - TWO ; $ff becomes ONE - TWO, 0 stays 0
-	add TWO       ; ONE - TWO becomes ONE, 0 becomes TWO
+	and FOO - BAR ; $ff becomes FOO - BAR, 0 stays 0
+	add BAR       ; FOO - BAR becomes FOO, 0 becomes BAR
 ```
 
 Or do:
@@ -150,25 +152,41 @@ Or do:
 ```asm
 	; 5 bytes, 5 cycles
 	sbc a         ; if carry, then $ff, else 0
-	and ONE ^ TWO ; $ff becomes ONE ^ TWO, 0 stays 0
-	xor TWO       ; ONE ^ TWO becomes ONE, 0 becomes TWO
+	and FOO ^ BAR ; $ff becomes FOO ^ BAR, 0 stays 0
+	xor BAR       ; FOO ^ BAR becomes FOO, 0 becomes BAR
 ```
 
-If `ONE` is 0 (i.e. set `a` to 0 if carry), then do:
+If `FOO` is 0 (i.e. set `a` to 0 if carry), then do:
 
 ```asm
 	; 4 bytes, 4 cycles
 	ccf     ; invert carry flag
 	sbc a   ; if originally carry, then 0, else $ff
-	and TWO ; 0 stays 0, $ff becomes TWO
+	and BAR ; 0 stays 0, $ff becomes BAR
 ```
 
-If `TWO` is 0 (i.e. set `a` to 0 if not carry), then do:
+If `BAR` is 0 (i.e. set `a` to 0 if not carry), then do:
 
 ```asm
 	; 3 bytes, 3 cycles
 	sbc a   ; if carry, then $ff, else 0
-	and ONE ; $ff becomes ONE, 0 stays 0
+	and FOO ; $ff becomes FOO, 0 stays 0
+```
+
+If `FOO` equals `BAR - 1`, then do:
+
+```asm
+	; 3 bytes, 3 cycles
+	sbc a   ; if carry, then $ff aka -1, else 0
+	add BAR ; -1 becomes BAR - 1 aka FOO, 0 becomes BAR
+```
+
+If `FOO` equals `BAR - 2`, then do:
+
+```asm
+	; 3 bytes, 3 cycles
+	sbc a    ; if carry, then $ff aka -1, else 0; doesn't change the carry flag
+	sbc -BAR ; -1 becomes BAR - 2 aka FOO, 0 becomes BAR
 ```
 
 
@@ -357,20 +375,20 @@ Don't do:
 
 ```asm
 	; 4 bytes, 4 cycles
-	ld b, ONE
-	ld c, TWO
+	ld b, FOO
+	ld c, BAR
 ```
 
 But do:
 
 ```asm
-	ld bc, ONE << 8 | TWO ; 3 bytes, 3 cycles
+	ld bc, FOO << 8 | BAR ; 3 bytes, 3 cycles
 ```
 
 Or better, use the `lb` macro in [macros/code.asm](../blob/master/macros/code.asm):
 
 ```asm
-	lb bc, ONE, TWO ; 3 bytes, 3 cycles
+	lb bc, FOO, BAR ; 3 bytes, 3 cycles
 ```
 
 
@@ -380,14 +398,14 @@ Don't do:
 
 ```asm
 	; 3 bytes, 4 cycles
-	ld a, CONST
+	ld a, FOOBAR
 	ld [hl], a
 ```
 
 But do:
 
 ```asm
-	ld [hl], CONST ; 2 bytes, 3 cycles
+	ld [hl], FOOBAR ; 2 bytes, 3 cycles
 ```
 
 
@@ -571,22 +589,26 @@ But do:
 
 ```asm
 	; 5 bytes, 8 cycles
+	(some code)
 	ld de, .return
 	push de
 	jp hl
 
-.return
-	...
+.return:
+	(some more code)
 ```
 
 But do:
 
 ```asm
-	call _hl_ ; 4 bytes, 7 cycles, counting the definition of _hl_
-	...
+	; 3 bytes, 6 cycles
+	; (4 bytes, 7 cycles, counting the definition of _hl_)
+	(some code)
+	call _hl_
+	(some more code)
 ```
 
-`_hl_` is a routine already defined in [home.asm](../blob/master/home.asm):
+`_hl_` is a routine already defined in [home/call_regs.asm](../blob/master/home/call_regs.asm):
 
 ```asm
 _hl_::