Sender: nate AT cartsys DOT com
Message-ID: <37698C10.1EA863E2@cartsys.com>
Date: Thu, 17 Jun 1999 17:00:16 -0700
From: Nate Eldredge <nate AT cartsys DOT com>
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To: djgpp AT delorie DOT com
Subject: Re: AT&T style asm problem
References: <01beb90f$e47e8f20$d1b2f1c3 AT scarfboy DOT tip DOT nl>
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Reply-To: djgpp AT delorie DOT com

Bart Alewijnse wrote:
> 
> Okay.. I'm modifying a sprite compiler for use in djgpp, and I dunno how to
> do the
> following.
> 
> I currently have
> fprintf(outfile," \"movb 0x%02X, 0x%X(%%%%edi,,)\\n\\t\" \n", byte1,
> offset);
> 
> that's in my C code. (extended asm, and the four %'s become two in the file
> that's
> written to.)That resoves to
>         "movb 0x12, 0x11D3(%%edi,,) \n\t"
> 
> The idea and the problem is the
> immed32(basepointer,indexpointer,indexscale)
> format. I dunno how to use it... (I never have before) edi contains the
> base screen
> pointer. Offset, which becomes the immed32 integer, is obviously the
> offset. What
> format do I use now? (I filled in constants for ease of reading)
> movb 0x12, 0x11D3(%%edi,$0,$0) ?
> movb 0x12, 0x11D3(,,%%edi) ?
> movb 0x12, 0x11D3($0,%%edi,$0) ?

The effective address for `disp(base,index,scale)' is

disp + base + (index * scale)

Where disp is a constant, base and index are registers, and scale is the
number 1, 2, 4 or (I think) 8.  (You don't need the $ delimiter in a
memory operand.)

Any of these can be omitted, and you need not include the delimiters for
omitted ones if they are at the end.  So:

disp
(base)
disp(base)
disp(base,index)  # scale assumed to be 1

but

disp(,index,scale) # must include the leading comma when omitting base

are all valid.

In your case, `0x1ed3(%edi)' is what you want, though `0x1ed3(,%edi)' or
`0x1ed3(,%edi,1)' would also work (though I think they might be larger
opcodes).
-- 

Nate Eldredge
nate AT cartsys DOT com