From: Hans-Bernhard Broeker <broeker AT physik DOT rwth-aachen DOT de>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: DJGPP Asm problems
Date: 15 Jun 2001 10:09:42 GMT
Organization: Aachen University of Technology (RWTH)
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birkoss <birkoss AT qhasecurity DOT com> wrote:

> I create some function in Asm, 

... and making your own life harder than it has to be, doing
so. Unlike some other DOS compilers, DJGPP doesn't force you to use
assembly whenever you want anything done efficiently --- it's clever
enough to be quite efficient if you just let it do a decent job, and
don't get into its way too much.

> void full_screen()
> {
>  __asm__ volatile("
>    pushl %eax\n

>    movb $00,%ah\n
>    movb $12,%al\n
>    int $0x10\n

>    popl %eax\n");
> }

As Eli already pointed out: Calling __dpmi_int() would have been a lot
easier, here.

> void point(int x_p, int y_p, int couleur_p)
> {
>  __asm__ volatile("
>    pushl %%eax\n
>         pushl %%ecx\n
>    pushl %%edx
>    movl %0,%%eax\n
>    movl %1,%%ecx\n
>    movl %2,%%edx\n
>    movb $0x0C,%%ah\n
>    int $0x10\n
>    popl %%edx\n
>    popl %%ecx\n
>    popl %%eax\n"
>    :
>    : "a" (couleur_p), "c" (x_p), "d" (y_p)

And this one is outright wrong, I think. You're mixing up extended
assembly (using input register descriptors) with simple assembly
("volatile" qualifier, and pushing all registers yourself). And this,
too, could have been done using __dpmi_int, instead.

Not even to mention that calling a BIOS interrupt to put a pixel to
screen is almost never a good idea. Not in plain 16bit DOS programs,
and even less so in 32bit protected mode ones made by DJGPP, which
have to do all kinds of magic behind the scenes to be able to call
16bit BIOS interrupts.

Directly accessing the framebuffer is going to be a lot faster than
any code similar to the above.
-- 
Hans-Bernhard Broeker (broeker AT physik DOT rwth-aachen DOT de)
Even if all the snow were burnt, ashes would remain.