RFR: 8189105: AARCH64: create intrinsic for sin and cos

[Andrew Haley]

On 06/20/2018 03:26 PM, Dmitrij Pochepko wrote:
> 
> 
> On 19.06.2018 20:46, Andrew Haley wrote:
>> On 06/18/2018 07:53 PM, Dmitrij Pochepko wrote:
>>> If you have any other ideas how to make the code easier to read and
>>> maintain I’m happy to improve it.
>> That's great!  Really, that's a vast improvement.  Excellent work.
>>
>> One or two relatively minor things:
>>
>> Why do you say the polynomial in kernel_sin/kernel_cos is a Taylor
>> series?  There's no such comment in sharedRuntimeTrig.cpp, and I doubt
>> it.  I would have thought it was a
>> least-maximum polynomial
>> approximation, not a Taylor series.
> Taylor series for cos(x) = 1 - x^2/2! + x^4/4! - x^6/6! + ... = 1 - 
> 0.5*x^2 + 4.16666666666666019037e-02 * x^4 - 1.38888888888741095749e-03 
> * x^6 ...
> so, if you take a look at kernel_cos function description you'll see 
> exactly same polynomial calculation with exactly same coefficients.

I don't think so.  I think the program uses

     4.16666666666666019037e-02, // c0x3FA555555555554C
    -1.38888888888741095749e-03, // 0xBF56C16C16C15177
     2.48015872894767294178e-05, // 0x3EFA01A019CB1590
    -2.75573143513906633035e-07, // 0xBE927E4F809C52AD
     2.08757232129817482790e-09, // 0x3E21EE9EBDB4B1C4
    -1.13596475577881948265e-11  // 0xBDA8FAE9BE8838D4

and unless I am mistaken the coefficients of the Taylor series for cos
are approximately

     4.16666666666666643537e-02,
    -1.38888888888888894189e-03,
     2.48015873015873015658e-05,
    -2.75573192239858882758e-07,
     2.08767569878681001866e-09,
    -7.81894280887451282427e-10,

>> What's the point of keeping the doubles in tables in hex form?
>> sharedRuntimeTrig.cpp doesn't do that, and it looks like obfuscation.
>> Even if you must keep them as hex, at least move the comment which
>> shows their true values next to their declaration, but I really can't
>> see the point.
> It was easier for me while debugging to use hex form. I changed 
> representation to double with hex form added in comment where applicable.

Excellent.

-- 
Andrew Haley
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
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