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From: tim@amdcad.AMD.COM (Tim Olson)
Newsgroups: comp.arch
Subject: Re: AM29000 Booleans
Message-ID: <16587@amdcad.AMD.COM>
Date: Thu, 7-May-87 12:07:22 EDT
Article-I.D.: amdcad.16587
Posted: Thu May  7 12:07:22 1987
Date-Received: Sat, 9-May-87 04:43:12 EDT
References: <1270@aw.sei.cmu.edu> <138@neptune.AMD.COM> <3540@spool.WISC.EDU>
Organization: Advanced Micro Devices, Inc., Sunnyvale, Ca.
Lines: 71

In article <3540@spool.WISC.EDU>, lm@cottage.WISC.EDU (Larry McVoy) writes:
> In article <138@neptune.AMD.COM> brian@neptune.AMD.COM (Brian McMinn) writes:
> >
> >No, this is not a typo.  All negative numbers are regarded as Boolean
> >TRUE.  Although this does not correspond with the "C" language
> >definition of TRUE, it did gain some speed in the hardware.  Since
> 
> Could you please show the assembly language generated for the following,
> 
> {	int x;
> 	
> 	if (x)
> 	    <stmt1>;
> 	else
> 	    <stmt2>;
> 
> 	if (!x)
> 	    <stmt1>;
> 	else
> 	    <stmt2>;
> }
> 
> And tell me which will be executed for x = -1, 0, 1.

I think you may be confusing Am29000 Booleans with 'C' Booleans.  They are
two different animals, and when code is generated from C programs, comparison
instructions (usually) must be used to create the correct Am29000 Boolean.
For example, the above code fragment compiles to:

---------------------------------------
	.global	_main
_main:
	.align

;	if (x)
	cpneq	gr72,gr70,0		<-- sets the msb of gr72 if gr70 != 0
	jmpf	gr72,$16		<-- jumps if the msb of gr72 is not set
	nop

;	    y = 0;
	jmp	$17			<-- remember those delayed branches!
	const	gr71,0
$16:
;	else
;	    y = 1;
	const	gr71,1
$17:

;	if (!x)
	cpeq	gr72,gr70,0
	jmpf	gr72,$18
	nop

;	    y = 0;
	jmp	$19
	const	gr71,0
$18:
;	else
;	    y = 1;
	const	gr71,1
$19:
	jmpi	lr00
	nop
----------------------------------------------
The code execution would be just what you expect (and what is required of C)
for all values of x.


	-- Tim Olson
	Advanced Micro Devices
	Processor Strategic Planning