Difference between revisions of "Z80 Good Programming Practices"
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If you have objects represented by adjacent chunks of data in memory, you can use IX to easily manage them. | If you have objects represented by adjacent chunks of data in memory, you can use IX to easily manage them. | ||
| + | <table border="1" cellpadding="2"> | ||
| + | <tr><th>Without</th><th>With</th></tr> | ||
| + | <tr> | ||
| + | <td> | ||
<nowiki> | <nowiki> | ||
ld b,10 | ld b,10 | ||
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djnz DisplaySpritesLoop | djnz DisplaySpritesLoop | ||
</nowiki> | </nowiki> | ||
| − | + | </td> | |
| + | <td> | ||
<nowiki> | <nowiki> | ||
COORDX equ. 0 | COORDX equ. 0 | ||
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djnz DisplaySpritesLoop | djnz DisplaySpritesLoop | ||
</nowiki> | </nowiki> | ||
| + | </td> | ||
| + | </tr> | ||
| + | </table> | ||
Defining constants for the offsets of each field of your "objects" makes the code more understandable. | Defining constants for the offsets of each field of your "objects" makes the code more understandable. | ||
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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. | 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. | ||
| − | + | <table border="1" cellpadding="2"> | |
| + | <tr><th>Without</th><th>With</th></tr> | ||
| + | <tr> | ||
| + | <td> | ||
<nowiki> | <nowiki> | ||
ld a,(SpriteNumber) | ld a,(SpriteNumber) | ||
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call SpriteRoutine | call SpriteRoutine | ||
</nowiki> | </nowiki> | ||
| − | + | </td> | |
| + | <td> | ||
<nowiki> | <nowiki> | ||
ld a,(SpriteNumber) | ld a,(SpriteNumber) | ||
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.dw Sprite4 | .dw Sprite4 | ||
</nowiki> | </nowiki> | ||
| + | </td> | ||
| + | </tr> | ||
| + | </table> | ||
And this one : | And this one : | ||
| − | + | <table border="1" cellpadding="2"> | |
| + | <tr><th>Without</th><th>With</th></tr> | ||
| + | <tr> | ||
| + | <td> | ||
<nowiki> | <nowiki> | ||
ld a,(MenuChoice) | ld a,(MenuChoice) | ||
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... | ... | ||
</nowiki> | </nowiki> | ||
| − | + | </td> | |
| + | <td> | ||
| + | |||
<nowiki> | <nowiki> | ||
ld a,(MenuChoice) | ld a,(MenuChoice) | ||
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.dw Choice4 | .dw Choice4 | ||
</nowiki> | </nowiki> | ||
| − | + | </td> | |
| − | + | </tr> | |
| + | </table> | ||
{{stub}} | {{stub}} | ||
Revision as of 06:43, 19 February 2006
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 jp (hl) ... CodeBranchLUT .dw Choice1 .dw Choice2 .dw Choice3 .dw Choice4 |
