RFR: 8375285: Port fdlibm asinh to Java [v8]

[Raffaello Giulietti]

On Wed, 4 Feb 2026 11:59:32 GMT, Anton Artemov <aartemov at openjdk.org> wrote:

>> Hi, please consider the following changes:
>> 
>> This is a port of FDLIBM asinh method.
>> 
>> Original C vs transliteration port:
>> 
>> 
>> $ diff -w fdlib_asinh.c Asinh.translit.java
>> 1c1,3
>> < /* asinh(x)
>> ---
>>> /**
>>> * Return the Inverse Hyperbolic Sine of x
>>> *
>> 2a5
>>> *
>> 10a14,17
>>> private static final class Asinh {
>>>       private static final double one = 1.0;
>>>       private static final double ln2 = 6.93147180559945286227e-01;
>>>       private static final double huge = 1.0e300;
>> 12,29c19
>> < #include "fdlibm.h"
>> <
>> < #ifdef __STDC__
>> < static const double
>> < #else
>> < static double
>> < #endif
>> < one =  1.00000000000000000000e+00, /* 0x3FF00000, 0x00000000 */
>> < ln2 =  6.93147180559945286227e-01, /* 0x3FE62E42, 0xFEFA39EF */
>> < huge=  1.00000000000000000000e+300;
>> <
>> < #ifdef __STDC__
>> <       double asinh(double x)
>> < #else
>> <       double asinh(x)
>> <       double x;
>> < #endif
>> < {
>> ---
>>>       static double compute(double x) {
>> 39c29
>> <           w = __ieee754_log(fabs(x))+ln2;
>> ---
>>>                       w = log(Math.abs(x))+ln2;
>> 41,42c31,32
>> <           t = fabs(x);
>> <           w = __ieee754_log(2.0*t+one/(sqrt(x*x+one)+t));
>> ---
>>>                       t = Math.abs(x);
>>>                       w = log(2.0*t+one/(sqrt(x*x+one)+t));
>> 45c35
>> <           w =log1p(fabs(x)+t/(one+sqrt(one+t)));
>> ---
>>>                       w =log1p(Math.abs(x)+t/(one+sqrt(one+t)));
>> 47a38
>>>       }
>> 
>> Transliteration port vs more idiomatic port:
>> 
>> 
>> $ diff -w Asinh.translit.java Asinh.fdlibm.java
>> 6,9c6,12
>> < *  Based on
>> < *    asinh(x) = sign(x) * log [ |x| + sqrt(x*x+1) ]
>> < *   we have
>> < *   asinh(x) := x  if  1+x*x=1,
>> ---
>>>  *
>>>  *      asinh(x) is defined so that asinh(sinh(alpha)) = alpha -INF < alpha < < INF
>>>  *      and sinh(asinh(x)) = x, -INF < x  < INF.
>>>  *      It can be written as asinh(x) = ln(x + sqrt(x^2 + 1)), -INF < x  < INF.
>>>  *      1. Replace x by |x| as the function is odd.
>>>  *      2.
>>>  *          asinh(x) := x, if 1+x^2 = 1,
>> 12a16,22
>>>  *
>>>  *
>>>  *
>>>  * Special cases:
>>>  *      only asinh(0)=0 is exact for finite x.
>>>  *      asinh(NaN) is NaN
>>>  *      asinh(INF) is INF
>> 14,15c24
>> < private static final class Asinh {
>> <       private static final double one = 1.0;
>> ---
>>> static final class Asinh {
>> 24c33,35
>> <               if(ix>=0x7ff00000) return x+x;  /* x is inf or NaN */
>> ---
>>>               if(ix >= 0x7ff00000) {
>>>                       return x...
>
> Anton Artemov has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8375285: Addressed reviewer's comments.

Hopefully the last nits.

src/java.base/share/classes/java/lang/FdLibm.java line 3531:

> 3529:      *
> 3530:      * Special cases:
> 3531:      *      only asinh(±0))=±0) is exact for finite x.

There are two `)` too much.

test/jdk/java/lang/Math/HyperbolicTests.java line 26:

> 24: /*
> 25:  * @test
> 26:  * @bug 4851625 4900189 4939441

Not sure if this requires the new bug ID.

test/jdk/java/lang/Math/HyperbolicTests.java line 1533:

> 1531: 
> 1532: 
> 1533:         for (int i = 0; i < testCases.length; i++) {

Why not enhanced `for`, like in the NaN loop below?

test/jdk/java/lang/Math/HyperbolicTests.java line 1712:

> 1710:     }
> 1711: 
> 1712:     public static int testAsinhCaseWithTolerance(double input,

This method is never invoked, IIUC.

test/jdk/java/lang/StrictMath/ExhaustingTests.java line 26:

> 24: /*
> 25:  * @test
> 26:  * @bug 8301833 8302026 8301444 8302028 8302040 8302027 8304028

Bug ID? Not sure.

test/jdk/java/lang/StrictMath/HyperbolicTests.java line 29:

> 27: /*
> 28:  * @test
> 29:  * @bug 4851625 8301444

Not sure if this requires the new bug ID.

-------------

PR Review: https://git.openjdk.org/jdk/pull/29273#pullrequestreview-3751044142
PR Review Comment: https://git.openjdk.org/jdk/pull/29273#discussion_r2764000347
PR Review Comment: https://git.openjdk.org/jdk/pull/29273#discussion_r2764034158
PR Review Comment: https://git.openjdk.org/jdk/pull/29273#discussion_r2764001683
PR Review Comment: https://git.openjdk.org/jdk/pull/29273#discussion_r2764002126
PR Review Comment: https://git.openjdk.org/jdk/pull/29273#discussion_r2764043243
PR Review Comment: https://git.openjdk.org/jdk/pull/29273#discussion_r2764039946