JDK 9 RFR of JDK-4851642: Add fused mac to Java math library

[Dmitry Nadezhin]

Hi Joe,

It looks good except a guard expression in the line Math:1550
(tmp == 0.0 && a == 0.0 || b == 0.0)
Variables a and b occur asymmetrically in this expression.
A symmetrical expression would be either
(a == 0.0 || b == 0.0)
or
(product.signum() == 0)

On Fri, Apr 15, 2016 at 3:14 AM, joe darcy <joe.darcy at oracle.com> wrote:

> Hello,
>
> In response to the review comments from Dmitry and Brian, I've prepared
> another iteration of the webrev:
>
>     http://cr.openjdk.java.net/~darcy/4851642.1/
>
> Summary of the changes:
>
> * Renamed the method to "fma" to follow the precedent of the C library.
> * Added API note citing IEEE 754 operation.
> * More test cases
> * More comments
> * Restructured handling of finite double value to be more straightforward.
>
> Thanks,
>
> -Joe
>
>
> On 4/12/2016 5:21 PM, joe darcy wrote:
>
>> Hello,
>>
>> Please review the changes for
>>
>>     JDK-4851642: Add fused mac to Java math library
>>     http://cr.openjdk.java.net/~darcy/4851642.0/
>>
>> Fused mac (multiply-accumulate) is a ternary floating-point operation
>> which accepts three inputs, a, b, c, and computes
>>
>>     a * b + c
>>
>> with a single rounding error rather than the usual two rounding errors (a
>> first for the multiply, a second one for the add). The fused mac operation
>> was added in the 2008 update to the IEEE 754 floating-point standard and
>> hardware support for the operation is becoming more and more common in
>> different processor families.
>>
>> When present as a hardware instruction, a fused mac can speed up loops
>> such as those for polynomial evaluation. A fused mac can also be used to
>> support a correctly rounding floating-point divide and support various
>> higher-precision operations such as "doubled-double" arithmetic.
>>
>> With the increasing availability of fused mac as a hardware primitive,
>> the time has come to add fused mac to the Java math library. Fused mac is
>> an ideal candidate to be intrinsified where hardware support is available.
>> However, this initial implementation does not attempt to add any such
>> intrinsics support in HotSpot; a follow-up RFE has been filed for that work
>> (JDK-8154122). The current library implementation favors code simplicity
>> over speed; a more performant implementation could be written by directly
>> decomposing the floating-point inputs rather than turning to BigDecimal and
>> may be written in the future. More extensive tests could be added in the
>> future as well.
>>
>> Thanks,
>>
>> -Joe
>>
>
>