RFR: JDK-8302040: Port fdlibm sqrt to Java [v2]

[Joe Darcy]

On Fri, 24 Feb 2023 13:19:36 GMT, Raffaello Giulietti <rgiulietti at openjdk.org> wrote:

>> src/java.base/share/classes/java/lang/FdLibm.java line 689:
>> 
>>> 687:             ix0 += (m << 20);
>>> 688:             z = __HI(z, ix0);
>>> 689:             z = __LO(z, ix1);
>> 
>> I was tempted to rewrite these line as something like:
>> `return Double.longBitsToDouble((long)ix0 << 32 | (long)ix1);`
>> and may do so in a future refactoring.
>
> That should read
> `return Double.longBitsToDouble((long)ix0 << 32 | ix1 & 0xffff_ffffL);`

Added new method to combine high and low. In a future refactoring pass, I'll use the method in other locations in FDLIBM where it is applicable.

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PR: https://git.openjdk.org/jdk/pull/12736