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

[Raffaello Giulietti]

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.

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PR: https://git.openjdk.org/jdk/pull/12800