English Amiga Board - I am trying to make my first GFX assembler code

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English Amiga Board (https://eab.abime.net/index.php)

- Coders. Tutorials (https://eab.abime.net/forumdisplay.php?f=73)

- - I am trying to make my first GFX assembler code (https://eab.abime.net/showthread.php?t=95154)

meynaf

08 December 2018 11:39

Quote:

Originally Posted by StingRay (Post 1289585)

You can use local labels. Though, the approach to use the stack to obtain the (string) addresses can indeed be quite useful.

Well, it's a real pain to disassemble (and to debug).
This program was just full of this and if i could kick the author's ass i'd have done it. :mad

litwr

08 December 2018 12:04

Quote:

Originally Posted by meynaf (Post 1289589)

Well, it's a real pain to disassemble (and to debug).
This program was just full of this and if i could kick the author's ass i'd have done it. :mad

Don't hack! :D

meynaf

08 December 2018 12:19

Quote:

Originally Posted by litwr (Post 1289597)

Don't hack! :D

Tell that to people who got happy with my game ports :cheese

StingRay

08 December 2018 18:31

Quote:

Originally Posted by meynaf (Post 1289589)

Well, it's a real pain to disassemble (and to debug).
This program was just full of this and if i could kick the author's ass i'd have done it. :mad

Well, nothing a simple MACRO in ReSource couldn't solve! :) Quite a few games actually use constructs like this (check the Wizkid code for a prime example) but I do agree, they are painful to debug/disassemble.

litwr

09 December 2018 11:06

I have the next sequence in my x86 code

Code:

     test [data],3

     jne label



    ...

data dw 0

How to do something similar with 68k? I could find out

Code:

    btst.w #0,data   ;or btst.b #0,data+1

    bne label



    btst.w #1,data

    bne label

And a bit shorter code

Code:

    move data,ccr

    bcc label

    bvc label

It is a bit odd that MOVE to CCR takes a word not a byte - it is not important, indeed.
Have I missed a better way? Thanks.

meynaf

09 December 2018 11:13

Quote:

Originally Posted by litwr (Post 1289749)

Have I missed a better way? Thanks.

Why not the obvious :

Code:

 moveq #3,d0

 and.w data,d0

 bne label

hooverphonique

10 December 2018 11:31

Quote:

Originally Posted by litwr (Post 1289749)

Code:

btst.w #0,data ;or btst.b #0,data+1

btst is always byte-sized when operating on memory!

StingRay

11 December 2018 10:21

And it doesn't have a size spezifier either, i.e. btst.w is wrong and any assembler which accepts that is broken IMHO.

litwr

14 December 2018 17:37

I have found out that Text call preserves A1 with A500 but corrupts it with A1200. :shocked

Leffmann

14 December 2018 18:08

D0-D1/A0-A1 are scratch registers, this has always been the case for system calls.

litwr

14 December 2018 20:50

Quote:

Originally Posted by Leffmann (Post 1290873)

D0-D1/A0-A1 are scratch registers, this has always been the case for system calls.

Thank you. I hoped that A1200 remains more compatible with A500 and was surprised when my code failed to work with A1200. I am going to follow documentation more strictly.

Don_Adan

14 December 2018 21:10

Quote:

Originally Posted by litwr (Post 1290897)

Thank you. I hoped that A1200 remains more compatible with A500 and was surprised when my code failed to work with A500. I am going to follow documentation more strictly.

Remember some Amiga ROM-s routines were reworked a few times. D0-D1/A0-A1 are always Amiga scratch registers, except a few math and exec routines (info is stored inside docs). Of course not always all scratch registers are used/changed.

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