RFR: 8365581: Optimize Java implementation of P256 arithmetic

[Chen Liang]

On Fri, 15 Aug 2025 01:01:01 GMT, Ben Perez <bperez at openjdk.org> wrote:

> There are several places where MontgomeryIntegerPolynomialP256.mult() can be optimized. In particular, since modulus[2] = 0 several multiplications can be removed. Other multiplications can be replaced by shifts, which also saves time. Preliminary tests indicate an improvement between 5-10%.

This particular method is already `@IntrinsicCandidate`: what special treatment does it get from the JVM?

I see you are inlining some modulus values manually. You can mark the arrays as `@Stable` and check what performance gain can you have as a result, because then C2 can treat these values as constants and generate more optimal computations.

-------------

PR Comment: https://git.openjdk.org/jdk/pull/26792#issuecomment-3190524045
PR Comment: https://git.openjdk.org/jdk/pull/26792#issuecomment-3191543014