RFR: JDK-8301205: Port fdlibm log10 to Java

[Raffaello Giulietti]

On Fri, 27 Jan 2023 06:52:31 GMT, Joe Darcy <darcy at openjdk.org> wrote:

> Restarting the port of FDLIBM to Java with the log10 method.
> 
> There are two port, the first a near-transliteration from C port to use as a test reference in
> 
> test/jdk/java/lang/StrictMath/FdlibmTranslit.java
> 
> and a more idiomatic Java port in 
> 
> src/java.base/share/classes/java/lang/FdLibm.java
> 
> First I debug the FdlibmTranslit port by running it against the C version. Once that is working, I copy the port into the java.lang.FdLibm.java and do a series of transformation to get the code closer to usual JDK style.

src/java.base/share/classes/java/lang/FdLibm.java line 820:

> 818:             hx = (hx & 0x000f_ffff) | ((0x3ff - i) << 20);
> 819:             y  = (double)(k + i);
> 820:             x = __HI(x, hx);

`            x = __HI(x, hx);  // replace high word of x with hx`

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PR: https://git.openjdk.org/jdk/pull/12242