RFR: 8341260: Add Float16 to jdk.incubator.vector [v10]

[Raffaello Giulietti]

On Tue, 29 Oct 2024 04:30:57 GMT, Joe Darcy <darcy at openjdk.org> wrote:

>> Port of Float16 from java.lang in the lworld+fp16 branch to jdk.incubabor.vector.
>
> Joe Darcy has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Add support for proper String -> Float16 conversion.

src/jdk.incubator.vector/share/classes/jdk/incubator/vector/Float16.java line 445:

> 443: 
> 444:         if (trialResult == 0.0 // handles signed zeros
> 445:             || Math.abs(trialResult) > (65504.0 + 32.0) || // Float.MAX_VALUE + ulp(MAX_VALUE)

Suggestion:

            || Math.abs(trialResult) > (65504.0 + 16.0) || // Float.MAX_VALUE + ulp(MAX_VALUE) / 2

src/jdk.incubator.vector/share/classes/jdk/incubator/vector/Float16.java line 504:

> 502:                     // without the period.
> 503:                     hexSignificand.append(s.substring(digitStart,      periodIndex));
> 504:                     hexSignificand.append(s.substring(periodIndex + 1, pIndex));

Suggestion:

                    hexSignificand.append(s, digitStart, periodIndex);
                    hexSignificand.append(s, periodIndex + 1, pIndex);

src/jdk.incubator.vector/share/classes/jdk/incubator/vector/Float16.java line 508:

> 506:                 } else {
> 507:                     // All integer digits, no fraction digits
> 508:                     hexSignificand.append(s.substring(digitStart, pIndex));

Suggestion:

                    hexSignificand.append(s, digitStart, pIndex);

src/jdk.incubator.vector/share/classes/jdk/incubator/vector/Float16.java line 549:

> 547:         long maskedValue = dAsLong & mask;
> 548:         // Can't have all-zeros or all-ones in low-order bits
> 549:         return maskedValue != 0L && maskedValue != mask;

Suggestion:

        long mask = 0x03FF_FFFF_FFFFL; // 42 low-order bits
        long maskedValue = dAsLong & mask;
        // not halfway between two adjacent Float16 values
        return maskedValue != 0x0200_0000_0000L;

I think this should be sufficient?

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

PR Review Comment: https://git.openjdk.org/jdk/pull/21574#discussion_r1820870830
PR Review Comment: https://git.openjdk.org/jdk/pull/21574#discussion_r1820870999
PR Review Comment: https://git.openjdk.org/jdk/pull/21574#discussion_r1820871061
PR Review Comment: https://git.openjdk.org/jdk/pull/21574#discussion_r1820871350