Z80 Good Programming Practices

Using IX

If you have objects represented by adjacent chunks of data in memory, you can use IX to easily manage them.

Without	With
ld b,10 ld hl,SpritesData DisplaySpritesLoop ld b,(hl) ; coordx inc hl ld c,(hl) ; coordy inc hl ld d,(hl) ; first part of address inc hl ld e,(hl) ; end of address inc hl call DisplaySprite djnz DisplaySpritesLoop	COORDX equ. 0 COORDY equ. 1 ADDR1 equ. 2 ADDR2 equ. 3 ld b,10 ld ix,SpritesData DisplaySpritesLoop ld b,(ix+COORDX) ld c,(ix+COORDY) ld d,(ix+ADDR1) ld e,(ix+ADDR2) call DisplaySprite ld hl,4 add ix,hl djnz DisplaySpritesLoop

Defining constants for the offsets of each field of your "objects" makes the code more understandable.

Lookup table

If you have a place in your code where a value is tested to choose between a lot of things, like subroutines or data, it can be a good idea to use lookup tables instead of a series of tests. It makes the code more readable, concise and extensible.

Without	With
ld a,(SpriteNumber) cp 1 jp z,ChooseSprite1 cp 2 jp z,ChooseSprite2 cp 3 jp z,ChooseSprite3 cp 4 jp z,ChooseSprite4 ... ChooseSprite1 ld hl,Sprite1 jp DisplaySprite ChooseSprite2 ld hl,Sprite2 jp DisplaySprite ChooseSprite3 ld hl,Sprite3 jp DisplaySprite ChooseSprite4 ld hl,Sprite4 jp DisplaySprite ... DisplaySprite ld bc,(coordinates) call SpriteRoutine	ld a,(SpriteNumber) add a,a ; a*2 ld h,O ld l,a ld de,SpriteAddressLUT add hl,de ld bc,(coordinates) call SpriteRoutine ... SpriteAddressLUT .dw Sprite1 .dw Sprite2 .dw Sprite3 .dw Sprite4

And this one :

Without	With
ld a,(MenuChoice) cp 1 jp z,Choice1 cp 2 jp z,Choice2 cp 3 jp z,Choice3 cp 4 jp z,Choice4 ...	ld a,(MenuChoice) add a,a ; a*2 ld h,O ld l,a ld de,CodeBranchLUT add hl,de bcall(_LdHLInd) jp (hl) ... CodeBranchLUT .dw Choice1 .dw Choice2 .dw Choice3 .dw Choice4

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