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
