[OpenPOWER-HDL-Cores] [Libre-soc-dev] Power ISA v3.0B FP "STORE" function, potential specification discrepancy

Luke Kenneth Casson Leighton lkcl at lkcl.net
Sun May 16 18:07:20 UTC 2021


On Sun, May 16, 2021 at 6:24 PM Jacob Lifshay <programmerjake at gmail.com> wrote:
>
> On Sat, May 15, 2021, 06:02 Luke Kenneth Casson Leighton <lkcl at lkcl.net>
> wrote:

> > should that be "FRS[12:63] = 0", testing the mantissa for zero?
> > or is it genuinely testing "both exponent and mantissa for zero"?
> >
>
> yes, it's both mantissa and exponent for zero, since that's +-0.0. if you
> tested just exponent for zero you'd miss sending subnormal f64 numbers
> through the rest of the algorithm.

ok cool - it's not documented / commented.  it works, but it's not explained
why.

l.


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