RFR: 8299576: Reimplement java.io.Bits using VarHandle access [v7]

[Uwe Schindler]

On Mon, 9 Jan 2023 10:33:44 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> Per Minborg has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Remove faulty test tag, improve other test tag, fix comments
>
> src/java.base/share/classes/java/io/Bits.java line 77:
> 
>> 75:         // Using Double.longBitsToDouble collapses NaN values to a single
>> 76:         // "canonical" NaN value
>> 77:         return Double.longBitsToDouble((long) LONG.get(b, off));
> 
> For the records, I believe the template classes for byte array var handle already perform this conversion - e.g.
> 
> 
> @ForceInline
>         static $type$ get(VarHandle ob, Object oba, int index) {
>             ArrayHandle handle = (ArrayHandle)ob;
>             byte[] ba = (byte[]) oba;
> #if[floatingPoint]
>             $rawType$ rawValue = UNSAFE.get$RawType$Unaligned(
>                     ba,
>                     ((long) index(ba, index)) + Unsafe.ARRAY_BYTE_BASE_OFFSET,
>                     handle.be);
>             return $Type$.$rawType$BitsTo$Type$(rawValue); // <-----------------------------
> #else[floatingPoint]
>             return UNSAFE.get$Type$Unaligned(
>                     ba,
>                     ((long) index(ba, index)) + Unsafe.ARRAY_BYTE_BASE_OFFSET,
>                     handle.be);
> #end[floatingPoint]
>         }
>  ````

For the other direction it uses the `floatToRawIntBits`: https://github.com/openjdk/jdk/blob/master/src/java.base/share/classes/java/lang/invoke/X-VarHandleByteArrayView.java.template#L148-L153

I think for symmatry we should keep it as is.

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PR: https://git.openjdk.org/jdk/pull/11840