NNTP-Posting-Date: Sat, 27 Oct 2012 14:06:31 -0500
From: Chris Hinsley <chris.hinsley@gmail.com>
Newsgroups: comp.lang.forth
Date: Sat, 27 Oct 2012 20:06:31 +0100
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On 2012-10-27 18:52:49 +0000, Rod Pemberton said:

> "Chris Hinsley" <chris.hinsley@gmail.com> wrote in message
> news:2012102717444755036-chrishinsley@gmailcom...
> 
>> One thing I just noticed is that NASM isn't encodeing small constant
>> adds as a single byte, it's useing the full 4 byte encodeing !
> 
> Old style NASM produced the most generic instruction encoding, i.e., large
> offsets.  With NASM, you need BYTE keyword for imm8 and maybe mem8
> encodings.  That's before H.P.A. started messing with NASM's syntax and made
> it more MASM like.  So, for new versions of NASM w/64-bit support, I'd check
> the manual for any syntax changes.
> 
> NASM requires you to specify data sizes when it's indeterminable from the
> instruction.  This is the opposite of assemblers like MASM where you use
> keywords to specify pointer types.  GAS (GCC) places sizes on the
> instruction name.  Unfortunately, that produces naming conflicts with Intel
> instructions names for a few instructions.
> 
>> I don't
>> recall there being an option to tell NASM to optimise constants, I
>> thought there was only -O flags to say optimize branches ?
>> 
> 
> Maybe, ask on comp.lang.asm.x86 or alt.lang.asm.
> 
> 
> Rod Pemberton

Thanks Rod, I found the relavent section in the NASM manual. You do 
need to specify 'byte' on constant loads of a 32bit reg from an imm8 ! 
So I changed my macro to do this:

	; adjust data stack
	%macro ADDDSP 1
		%if ((%1 >= -128) && (%1 < 128))
			add ebp, byte %1
		%else
			add ebp, %1
		%endif
	%endm

This has shorten quite a few words ! :)

Chris