From: "Tom St Denis" <tomstdenis AT yahoo DOT com>
Newsgroups: comp.os.msdos.djgpp
References: <5BF60CD649EDD411A04600B0D049F53A544468 AT hydmail02 DOT hyd DOT wilco-int DOT com>
Subject: Re: Accessing registers from C
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Date: Mon, 02 Jul 2001 11:30:04 GMT
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"Prashant Ramachandra" <rprash AT wilco-int DOT com> wrote in message
news:5BF60CD649EDD411A04600B0D049F53A544468 AT hydmail02 DOT hyd DOT wilco-int DOT com...
> On Monday, July 02, 2001 9:03 AM, Tom St Denis [SMTP:tomstdenis AT yahoo DOT com]
> wrote:
> |
> | > Everytime you use the variable "eax", you're actually accessing
> | > or
> | modifying
> | > the eax register itself.
> |
> | Perhaps, and by doing so you take away chances for GCC to optimize
> | the code.
>
> Yes, but it's useful in certain cases. I posted some code to check the CPU
> type back in 1998. That's the simplest use I can think of. You might want
to
> see that. And the linux kernel uses lots of this, too. Do you think they
> weren't concerned about optimizing ther kernel code?
>
> | You might as well not write in C then.
>
> You won't be using this in every function. So this doesn't justify
anything.

Typically unless your function is an inline [say like a fixed point
multiplication, etc] writting asm statements in C is a bad idea.  It leads
to poor messy code that is hard to maintain.

Ideally all of your .C code is C code and you just have #ifdefs to excluded
functions for which you have assembler equivalents.

Tom