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

[Andrey Turbanov]

On Wed, 1 Mar 2023 05:28:34 GMT, Joe Darcy <da...@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 519:

> 517:                 //  compute -1.0/(x + r) accurately
> 518:                 double a,t;
> 519:                 z  = w;

Suggestion:

                z = w;

src/java.base/share/classes/java/lang/FdLibm.java line 521:

> 519:                 z  = w;
> 520:                 z = __LO(z, 0);
> 521:                 v  = r - (z - x);   // z + v = r + x

Suggestion:

                v = r - (z - x);   // z + v = r + x

src/java.base/share/classes/java/lang/FdLibm.java line 524:

> 522:                 t = a  = -1.0/w;    // a = -1.0/w
> 523:                 t = __LO(t, 0);
> 524:                 s  = 1.0 + t*z;

Suggestion:

                s = 1.0 + t*z;

src/java.base/share/classes/java/lang/FdLibm.java line 641:

> 639:                             w  = fn*pio2_3;
> 640:                             r  = t - w;
> 641:                             w  = fn*pio2_3t - ((t - r) - w);

let's either align assignments with following `y[0] = r - w;` or remove 
redundant space before `=`

src/java.base/share/classes/java/lang/FdLibm.java line 664:

> 662:             // set z = scalbn(|x|,ilogb(x)-23)
> 663:             z = __LO(z, __LO(x));
> 664:             e0  = (ix >> 20) - 1046;        /* e0 = ilogb(z)-23; */

Suggestion:

            e0 = (ix >> 20) - 1046;        /* e0 = ilogb(z)-23; */

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