[libre-riscv-dev] [isa-dev] Re: FP transcendentals (trigonometry, root/exp/log) proposal

Bruce Hoult brucehoult at sifive.com
Fri Aug 9 09:12:00 BST 2019

On Fri, Aug 9, 2019 at 12:40 AM lkcl <luke.leighton at gmail.com> wrote:
> On Friday, August 9, 2019 at 8:25:54 AM UTC+1, andrew wrote:
>>> Andrew: I appreciate that you're busy
>> Good point - I capitulate.
> Andrew!  that doesn't help!  your input here is just as valuable as everyone else's.  if you believe you have a better idea *it's important to evaluate it*!

It's not Andrew's job to come up with a better idea. It's your job.

The key word is "quantitative". You, as the proposer of new
instructions must provide justification for the percentage improvement
of having the new instruction vs not having it. Not hand-waving.
Numbers. Measured, or at least calculated in a justifiable way.

If there is a measurable and significant improvement on some large
body of code, such as SPEC for example, then that would be grounds for
considering inclusion in a RISC-V Foundation standard extension.

If it improves only some narrow specialized task then that might
justify a custom extension. But you haven't even shown that, other
than "hardware good -- software bad". Is it even measurable, even on
*your* workload? We sure don't know the answer.

Potential market size is irrelevant The most it does is provide
justification for doing the quantitative performance evaluation in the
first place.

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