Sender: nate AT cartsys DOT com
Message-ID: <36634667.C344DF85@cartsys.com>
Date: Mon, 30 Nov 1998 17:29:11 -0800
From: Nate Eldredge <nate AT cartsys DOT com>
X-Mailer: Mozilla 4.05 [en] (X11; I; Linux 2.0.35 i486)
MIME-Version: 1.0
To: djgpp AT delorie DOT com
Subject: Re: misc questions
References: <ranla DOT 132 DOT 00089E39 AT post DOT tau DOT ac DOT il>
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Reply-To: djgpp AT delorie DOT com

Tal Lavi wrote:
> 
> Just a couple of misc questions, thanks in advance:
> 
> 1)Can I define an extended asm command as a macro,
> with one of the outputs value returned?

You can, using GCC's statement-expressions extension.  Example:

#define TEST_BIT(n, b) ({  		\
	char c;				\
	asm("btl %1, %2; "		\
	    "setcb %0"     		\
	    : "=rm" (c)			\
	    : "rI" (b), "rm" (n));	\
	c;				\
})

See also the info nodes "Statement Exprs" and "Extended Asm" in the GCC
docs.

> 2)I need to access a word size union in two forms: as the entire 16-bit word,
> and as the first 5 bits, next 6 and last 5.
> Can this be done in DJGPP?

You can try:

union word {
   unsigned short s;
   struct {
      unsigned low : 5;
      unsigned mid : 6;
      unsigned high : 5;
   } bits;
};

I'm not sure what order GCC allocates bitfields in, so that might be
wrong.

You can also do some macros with shifting and masking; that will also be
more portable.
-- 

Nate Eldredge
nate AT cartsys DOT com