RFR: 8265768 [aarch64] Use glibc libm impl for dlog, dlog10, dexp iff 2.29 or greater on AArch64.

[Andrew Haley]

On Thu, 29 Apr 2021 20:24:25 GMT, Carlos O'Donell <github.com+3019228+codonell at openjdk.org> wrote:

> Where does the requirement for monotonicity come from?

Semi-monotonicity, to be precise. In the spec of java.lang.Math,

"Besides accuracy at individual arguments, maintaining proper relations between the method at different arguments is also important. Therefore, most methods with more than 0.5 ulp errors are required to be semi-monotonic: whenever the mathematical function is non-decreasing, so is the floating-point approximation, likewise, whenever the mathematical function is non-increasing, so is the floating-point approximation. Not all approximations that have 1 ulp accuracy will automatically meet the monotonicity requirements."

I wouldn't be surprised if the approximations we need in glibc meet this anyway. We just need to check.

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PR: https://git.openjdk.java.net/jdk/pull/3510