RFR: JDK-8302027: Port fdlibm trig functions (sin, cos, tan) to Java

[Joseph D. Darcy]

On 3/1/2023 8:16 AM, Raffaello Giulietti wrote:
> On Wed, 1 Mar 2023 14:27:09 GMT, Andrey Turbanov <aturbanov at openjdk.org> wrote:
>
>>> Last and certainly not least in the port of FDLIBM to Java, the transcendental methods for sin, cos, and tan.
>>>
>>> Some more tests are to be written in the StrictMath directory to verify that the StrictMath algorihtm for sin/cos/tan is being used rather than a different one. However, I wanted to get the rest of the change out for review first.
>>>
>>> The sin/cos/tan methods are grouped together since they share the same argument reduction logic. Argument reduction is the process of mapping an argument of a function to an argument in a restricted range (and possibly returning some function of the reduced argument). For sin, cos, and tan, since they are fundamentally periodic with respect to a multiple of pi, argument reduction is done to find the remainder of the original argument with respect to pi/2.
>> src/java.base/share/classes/java/lang/FdLibm.java line 814:
>>
>>> 812:
>>> 813:         static final double
>>> 814:             twon24  = 0x1.0p-24; // 5.96046447753906250000e-08
>> Suggestion:
>>
>>              twon24 = 0x1.0p-24; // 5.96046447753906250000e-08
> Would it be worthwhile to declare this as a compile time constant, similarly to `TWO24`? If it's used only here, then probably not.

That particular constant is only used to implement one method. Since  
TWO24 is used in two of the methods being ported in this PR, I pulled it 
out. (As I may have mentioned before, once all the FDLIBM methods are 
ported, I plan to make a few cleanup passes over the code, including 
pulling out any other common constants, etc.)

-Joe