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Re: iso c9x unordered fp cmp builtins
- To: Richard Henderson <rth at cygnus dot com>
- Subject: Re: iso c9x unordered fp cmp builtins
- From: David Edelsohn <dje at watson dot ibm dot com>
- Date: Mon, 02 Mar 1998 00:51:22 -0500
- Cc: egcs at cygnus dot com
>>>>> Richard Henderson writes:
>> Did your SPARC implementation *change* the use of those two FP
>> compare instructions?
Richard> Not with respect to normal comparisions, no. That is, normal comparisons
Richard> do signal qnan, and as far as I can tell, always have.
The "rs6000" port always has used fcmpu and never has signal QNaN.
This also is the behavior of IBM's XLC. Does iso9x now mandate that the
regular comparison operators signal QNaN? Using the fcmpo instruction and
enabling one of the varying exactness degrees of QNaN signalling in the
PowerPC FP control register imposes a performance degradation (which I
think is why it is not used by default).