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Re: Support for MIPS r5900
"Maciej W. Rozycki" <macro@codesourcery.com> writes:
>> I tested the calculation with the type "float".
>> ABI o32 with -mhard-float and -msingle-float produces the following results:
>> 1.000000 (0x3f800000) / 0.000000 (0x00000000) = nan (0x7fffffff)
>> 0.000000 (0x00000000) / 0.000000 (0x00000000) = nan (0x7fffffff)
>> 0.000000 (0x00000000) / nan (0x7fc00000) = 0.000000 (0x00000000)
>> 1.000000 (0x3f800000) + 1.000000 (0x3f800000) = 2.000000 (0x40000000)
>> 1.000000 (0x3f800000) + inf (0x7f800000) = inf (0x7f800000)
>> inf (0x7f800000) + inf (0x7f800000) = nan (0x7fffffff)
>> inf (0x7f800000) + -inf (0xff800000) = 0.000000 (0x00000000)
>> nan (0x7fc00000) + nan (0x7fc00000) = nan (0x7fffffff)
>> nan (0x7fc00000) + nan (0xffc00000) = 0.000000 (0x00000000)
>>
>> The r5900 manual calls the result of 0/0 Fmax. So 0x7fffffff seems to be Fmax.
>
> So presumably you can get 0x7fffffff as an arithmetic result of a
> calculation involving regular numbers as well, right? Say 0x7f7ffffe +
> 0x74000000 (using the binary-encoded notation)? That would be beyond the
> IEEE-754 single range.
Yeah, if I recall correctly. We already support what I think is the
same format for SPU (spu_single_format), which I suppose makes sense
given its heritage. Hopefully the format itself won't need much
work in GCC.
Richard