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From: mcdonald@uxe.cso.uiuc.edu
Newsgroups: comp.lang.c
Subject: Re: iAPX86 code for ABS (using Microsof
Message-ID: <225800188@uxe.cso.uiuc.edu>
Date: 19 Jun 89 12:30:00 GMT
References: <1202@draken.nada.kth.se>
Lines: 27
Nf-ID: #R:draken.nada.kth.se:1202:uxe.cso.uiuc.edu:225800188:000:759
Nf-From: uxe.cso.uiuc.edu!mcdonald    Jun 19 07:30:00 1989


>I remember a review of Microsoft's C compiler for MS-DOS that stated it
>produced no-conditional-jump-abs-code. The function to convert an integer
>to a positive integer was performed without a conditional jump (i.e. JS or
>something). I'm very interested in this piece of code, so if someone
>who does have a Microsoft C-compiler could try something like
>  main()
>  { int a,b;
>    a=-10;
>    b=abs(a);
>  }

Here is the result of cl -c -Ox -Fa test.c, excluding the header and trailer:

; a = -10
	mov	WORD PTR [bp-2],-10	;a
; b = abs(a)
	mov	ax,-10
	cwd	
	xor	ax,dx
	sub	ax,dx
	mov	WORD PTR [bp-4],ax	;b

So your review was correct!  I assume that they do this odd thing in
order to not empty instruction prefetch queues????????????????

Doug McDonald