[LLVMdev] a question about constant fold for fdiv

[Jeff Cohen]

Reid Spencer wrote:
> On Thu, 2007-03-22 at 15:50 -0700, leo han wrote:
>   
>> Hello, I have a question about the constant folding for fdiv instructions. 
>> For the instruction "fdiv double 0.0, 0.0", the folded result is inf. I 
>> think this should be nan. Can anyone tell me why it is not nan?
>>     
>
> I think the specification says that it is "undefined" so any value will
> do. inf is just as undefined as nan.
>
> Reid.

In IEEE Std 754-1985, subclause 7.2- Division by Zero, it says:

/"If the divisor is zero and the dividend is a finite nonzero number, 
then the division by zero shall be signaled. The result, when no trap 
occurs, shall be a correctly signed (infinity symbol)(6.3)."

/So LLVM is correct (assuming it handles signs correctly).
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