[lworld+fp16] RFR: 8334432: Refine Float16.fma

[Joe Darcy]

On Fri, 5 Jul 2024 12:33:29 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

> My query was in following context, citing excerpt from JVM Specification 22 section 2.11.3.
> 
> "The Java Virtual Machine does not indicate overflow or underflow during operations on floating-point data types. That is, floating-point instructions never cause the Java Virtual Machine to throw a run-time exception (not to be confused with an IEEE 754 floating-point exception). **An operation that overflows produces a signed infinity; an operation that underflows produces a subnormal value or a signed zero;** an operation that has no unique mathematically defined result produces NaN. All numeric operations with NaN as an operand produce NaN as a result"

Sure; that is reasonable.

The correctness of the Float16.fma method relies on the correctness of the double to Float16 conversion. As part of a larger test update, I was planned on expanding the double to Float16 testing. In particular, a test methodology like:

For each finite Float16 value, test the double values around the half-way point to make sure the rounding is correct in those cases. Since there are so few Float16 values, I expect this test to run quickly.

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PR Review Comment: https://git.openjdk.org/valhalla/pull/1143#discussion_r1667420329