Re: [PATCH] Fix abs.[sd] and neg.[sd] emulation for NaN operands

[Chris Dearman <chris@mips.com>]

Atsushi Nemoto wrote:
> Excuse me for too late comment.
> 
> On Mon, 12 Oct 2009 14:57:18 -0700, Chris Dearman <chris@mips.com> wrote:
>> From: Nigel Stephens <nigel@mips.com>
>>
>> This patch ensures that the sign bit is always updated
>> for NaN operands.
> ...
>> @@ -76,15 +74,12 @@ ieee754dp ieee754dp_abs(ieee754dp x)
>>  	CLEARCX;
>>  	FLUSHXDP;
>>  
>> +	/* Clear sign ALWAYS, irrespective of NaN */
>> +	DPSIGN(x) = 0;
>> +
>>  	if (xc == IEEE754_CLASS_SNAN) {
>> -		SETCX(IEEE754_INVALID_OPERATION);
>> -		return ieee754dp_nanxcpt(ieee754dp_indef(), "neg");
>> +		return ieee754dp_nanxcpt(ieee754dp_indef(), "abs");
>>  	}
>>  
>> -	if (ieee754dp_isnan(x))	/* but not infinity */
>> -		return ieee754dp_nanxcpt(x, "abs", x);
>> -
>> -	/* quick fix up */
>> -	DPSIGN(x) = 0;
>>  	return x;
>>  }
> 
> Is there any reason for removal of SETCX(IEEE754_INVALID_OPERATION)
> line here?
> 
> The older version of this fix ("Fix absd emulation" by Raghu Gandham)
> did not remove the line.
> 
> Without this line, a signaling NaN will not raise a signal.  It seems
> not expected behaviour.

ieee754dp/sp_nanxcpt also sets the invalid exception bit so I think this 
is duplicated code. I think the same fix should have been applied to 
ieee754sp_neg/ieee754dp_neg for consistency.

Chris

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