From: Shawn Hargreaves <Shawn AT talula DOT demon DOT co DOT uk>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: info, FAQ not enough -> GCC and ASM
Date: Tue, 11 Mar 1997 18:51:55 +0000
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SteelGolem writes:
>what i don't understand is how you put them in the registers 
>ax/bx/eax/etc.. is it possible to access the registers? (i know, i know, 
>its protected mode..)

Look in "info gcc machine constraints machine", at the Intel 386
section. You have to realise that the info docs apply to gcc on any
platform, so machine-specific registers like eax aren't included in the
main body of the text.

Briefly, the register-specific constraints are:

    a = eax
    b = ebx
    c = ecx
    d = edx
    S = esi
    D = edi

>or at least, convert the following borland c function:

I found the best way of learning the gcc asm syntax was to read as much
example code as I could get my hands on: in particular the contents of
include/sys/farptr.h are well worth taking a look at.

If you are after a fixed point multiply routine, look at the fmul()
function in allegro.h. It's a bit more complicated than your example
because it checks for overflows, and it uses 16.16 format numbers rather
than 24.8, but the same principles apply.


/*
 *  Shawn Hargreaves - shawn AT talula DOT demon DOT co DOT uk - http://www.talula.demon.co.uk/
 *  Beauty is a French phonetic corruption of a short cloth neck ornament.
 */