Hi Paul, Thank you so much for this complete summary !
I will still perform some benchmarks and could port acos native code into java code as it is used by marlin. Anyway I will backport the Cbrt java code into Marlin @ github for JDK8 users (GPL v2). Thanks, Laurent Le 9 nov. 2017 18:19, "Paul Sandoz" <paul.san...@oracle.com> a écrit : > Hi Laurent, > > A Java method is a candidate for intrinsification if it is annotated with > @HotSpotIntrinsicCandidate. When running Java code you can also use the > HotSpot flags -XX:+PrintCompilarion -XX:+PrintInlining to show methods that > are intrinsic (JIT watch, as mentioned, is also excellent in this regard). > > I recommend cloning OpenJDK and browsing the source. > > Some of the math functions are intrinsic in the interpreter and all the > runtime compilers to ensure consistent results across interpretation and > compilation. > > Work was done by Intel to improve many of the math functions. See: > > Update for x86 sin and cos in the math lib > https://bugs.openjdk.java.net/browse/JDK-8143353 > > Update for x86 pow in the math lib > https://bugs.openjdk.java.net/browse/JDK-8145688 > > (From these you can track related issues.) > > Other Math functions are not intrinsic like cbrt (non-native) and acos > (native). There is ongoing work to turn native implementations into Java > implementations (i don’t know if there would be any follow up on > intrinsification). > > https://bugs.openjdk.java.net/browse/JDK-8134780 > https://bugs.openjdk.java.net/browse/JDK-8171407 > > Joe knows more. > > — > > As part of the Vector API effort we will likely need to investigate the > support for less accurate but faster math functions. It’s too early to tell > if something like a FastMath class will pop out of that, but FWIW i am > sympathetic to that :-) > > I liked this tweet: > > https://twitter.com/FioraAeterna/status/926150700836405248 > > life as a gpu compiler dev is basically just fielding repeated > complaints that > "fast math" isn't precise and "precise math" isn't fast > > as an indication of what we could be getting into :-) > > Paul. > > > On 9 Nov 2017, at 01:00, Laurent Bourgès <bourges.laur...@gmail.com> > wrote: > > > > Hi, > > > > The Marlin renderer (JEP265) uses few Math functions: sqrt, cbrt, acos... > > > > Could you check if the current JDK uses C2 intrinsics or libfdm (native / > > JNI overhead?) and tell me if such functions are already highly optimized > > in jdk9 or 10 ? > > > > Some people have implemented their own fast Math like Apache Commons Math > > or JaFaMa libraries that are 10x faster for acos / cbrt. > > > > I wonder if I should implement my own cbrt function (cubics) in pure java > > as I do not need the highest accuracy but SPEED. > > > > Would it sound possible to have a JDK FastMath public API (lots faster > but > > less accurate?) > > > > Do you know if recent CPU (intel?) have dedicated instructions for such > > math operations ? > > Why not use it instead? > > Maybe that's part of the new Vectorization API (panama) ? > > > > Cheers, > > Laurent Bourges > >
