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

Wed Apr 28 10:34:51 UTC 2021

On Wed, 28 Apr 2021 09:25:01 GMT, Andrew Haley <aph at openjdk.org> wrote:

> Re monotonicity: all is not necessarily lost. There's a theorem due to Ferguson and Brightman which says that
> 
> ```
> if
>          abs(f(m+) - f(m))
> eps < -----------------------
>       abs(f(m+)) + abs(f(m))'
> 
> for all m, the approximation is monotone.
> 
> m is the machine number, m+ its successor
> eps the maximum relative error of the approximation f(m)
> ```
> 
> See
> http://www-leland.stanford.edu/class/ee486/doc/ferguson1991.pdf, particularly the Appendix, which contains a table of expressions for the five basic transcendental functions.

We can definitely be checked for single precision! I am uncertain how much water that would hold.

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