Copied Jeff's Tips, WikiTI to come

1 files changed, 159 insertions, 3 deletions

diff --git a/Optimizing-assembly-code.md b/Optimizing-assembly-code.md
index 6f61867..7477c2e 100644
--- a/Optimizing-assembly-code.md
+++ b/Optimizing-assembly-code.md
@@ -1,7 +1,163 @@
-## TOC
+Most tricks come from either [Jeff's GB Assembly Code Tips v1.0](http://www.devrs.com/gb/files/asmtips.txt), or [the page on Z80 Optimization on WikiTI](http://wikiti.brandonw.net/index.php?title=Z80_Optimization)
 
+## Registers
 
-TODO
+### Set A to zero
+```asm
+	ld a, 0 ; 2 bytes, 2 cycles, no changes to flags
 
+;;;
 
-Many of [these techniques for Z80 optimization](http://wikiti.brandonw.net/index.php?title=Z80_Optimization) are still applicable to GBZ80 code, even with its reduced registers and instructions.
+	xor a ; 1 byte, 1 cycle, sets flags C to 0 and Z to 1
+	sub a ; 1 byte, 1 cycle, sets flags C to 0 and Z to 1
+```
+
+### Set A to some constant subtracted by A
+```asm
+	ld b,a ; 4 bytes, 4 cycles
+	ld a,CONST
+	sub b
+
+;;;
+
+	cpl ; 3 bytes, 3 cycles
+	add CONST+1
+```
+
+### Add A to HL
+```asm
+	add l ; 6 bytes, 6 cycles
+	ld l, a
+	ld a, 0
+	adc h
+	ld h,a
+
+;;;
+
+	add l ; 5 bytes, 5 cycles
+	ld l, a
+	jr nc, .NoCarry
+	inc h
+
+.NoCarry:
+```
+
+### Loading from an offset to HL
+```asm
+	ld a, [offset] ; 8 bytes, 10 cycles
+	ld l, a
+	ld a, [offset+1]
+	ld h, a
+
+;;;
+
+	ld hl, offset ; 6 bytes, 8 cycles
+	ld a, [hli]
+	ld h, [hl]
+	ld l, a
+```
+
+### Exchanging HE and DL
+```asm
+	ld a,d ; 6 bytes, 6 cycles
+	ld d,h
+	ld h,a
+	ld a,e
+	ld e,l
+	ld l,a
+
+;;;
+
+	push de ; 4 bytes, 9 cycles
+	ld d,h
+	ld e,l
+	pop hl
+```
+
+## Branching
+
+### Compare A to zero
+```asm
+	cp 0 ; 2 bytes, 2 cycles
+
+;;;
+
+	or a ; 1 byte, 1 cycle
+	and a ; 1 byte, 1 cycle
+```
+
+### Compare A-1 to zero
+```asm
+	cp 1 ; 2 bytes, 2 cycles
+
+;;;
+
+	dec a ; 1 byte, 1 cycle, decrements a
+```
+
+## Functions
+
+### Tail call optimization
+```asm   
+	call Function ; 4 bytes, 10 cycles
+	ret
+
+;;;
+
+	jp Function ; 3 bytes, 4 cycles
+```
+
+## Executing subroutines
+```asm
+	ld hl, param1
+	call Function1
+	ld hl, param2
+	call Function2
+	ld hl, param3
+	call Function1
+	...
+	...
+
+.Function1:
+	...
+	ret
+.Function2:
+	...
+	ret
+	
+;;;
+
+	ld sp, calltable
+	ret ; jump to sp (first entry on calltable)
+
+.Function1:
+	pop hl
+	...
+	ret
+.Function2:
+	pop hl
+	...
+	ret
+
+calltable:
+	dw Function1, param1
+	dw Function2, param2
+	dw Function1, param3
+```
+
+### Calling HL
+```asm
+	ld de, .retadr ; 5 bytes, 8 cycles
+	push de
+	jp [hl]
+	.retadr:
+	...
+
+;;;
+
+	call DoJump ; 4 bytes, 7 cycles
+	...
+
+DoJump:
+	jp [hl]
+```
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