On Thu, 15 Apr 2021 08:33:47 GMT, gregcawthorne <github.com+73799211+gregcawtho...@openjdk.org> wrote:
> Glibc 2.29 onwards provides optimised versions of log,log10,exp. > These functions have an accuracy of 0.9ulp or better in glibc > 2.29. > > Therefore this patch adds code to parse, store and check > the runtime glibcs version in os_linux.cpp/hpp. > This is then used to select the glibcs implementation of > log, log10, exp at runtime for c1 and c2, iff we have > glibc 2.29 or greater. > > This will ensure OpenJDK can benefit from future improvements > to glibc. > > Glibc adheres to the ieee754 standard, unless stated otherwise > in its spec. > > As there are no stated exceptions in the current glibc spec > for dlog, dlog10 and dexp, we can assume they currently follow > ieee754 (which testing confirms). As such, future version of > glibc are unlikely to lose this compliance with ieee754 in > future. > > W.r.t performance this patch sees ~15-30% performance improvements for > log and log10, with ~50-80% performance improvements for exp for the > common input ranged (which output real numbers). However for the NaN > and inf output ranges we see a slow down of up to a factor of 2 for > some functions and architectures. > > Due to this being the uncommon case we assert that this is a > worthwhile tradeoff. Where does the requirement for monotonicity come from? ------------- PR: https://git.openjdk.java.net/jdk/pull/3510
