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

[Luis Vitorio Cargnini]

Hello,

My $0.02 of contribution
Regarding the comment of 3 platforms:
> * Embedded Platform (where it's entirely up to the implementor, as there
will be no interaction with public APIs)
No, IEEE, ARM is an embedded platform and they implement IEEE in all of them
> * UNIX Platform (which would require strict IEEE754 accuracy, for use in
GNU libm, OR repeatable numericalist-acceptable accuracy)
Standard IEEE, simple no 'new' on this sector.
> * a *NEW* 3D Platform, where accuracy is defined by strict conformance to
a high-profile standard e.g. OpenCL / Vulkan.
No, simply use IEEE that it is all, and based on the IEEE standard you can
measure the deviation in your system.


No, just adopt IEEE-754, it is a standard, it is a standard for a reason.
Anything out of IEEE-754, it does not conform with IEEE and for such you
are on your own. However, you still can demonstrate your deviation from the
standard.


Best Regards,
Luis Vitorio Cargnini, Ph.D.
Senior Hardware Engineer
OURS Technology Inc., Santa Clara, California, 95054


On Wed, Aug 7, 2019 at 10:20 PM lkcl <luke.leighton at gmail.com> wrote:

>
>
> On Thursday, August 8, 2019 at 2:17:37 AM UTC+1, MitchAlsup wrote:
>>
>> An old guy at IBM (a Fellow) made a long and impassioned plea in a paper
>> from the late 1970s or early 1980s that whenever something is put "into the
>> instruction set" that the result be as accurate as possible. Look it up,
>> it's a good read.
>>
>> At the time I was working for a mini-computer company where a new
>> implementation was not giving binary accurate results compared to an older
>> generation. This was traced to an "enhancement" in the F32 and F64 accuracy
>> from the new implementation. To a customer, they all wanted binary
>> equivalence, even if the math was worse.
>>
>
> someone on the libre-riscv-dev list just hilariously pointed out that
> Ahmdahl-compatible IBM370 had FP that was more accurate than the 370:
> customers *complained* and they had to provide libraries that
> *de-accurified* the FP calculations :)
>
> My gut feeling tell me that the numericalists are perfectly willing to
>> accept an error of 0.51 ULP RMS on transcendental calculations.
>> My gut feeling tell me that the numericalists are not willing to accept
>> an error of 0.75 ULP RMS on transcendental calculations.
>> I have no feeling at all on where to draw the line.
>>
>
> this tends to suggest that three platform specs are needed:
>
> * Embedded Platform (where it's entirely up to the implementor, as there
> will be no interaction with public APIs)
> * UNIX Platform (which would require strict IEEE754 accuracy, for use in
> GNU libm, OR repeatable numericalist-acceptable accuracy)
> * a *NEW* 3D Platform, where accuracy is defined by strict conformance to
> a high-profile standard e.g. OpenCL / Vulkan.
>
> l.
>
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