RFR: 8365581: Optimize Java implementation of P256 arithmetic [v3]

[Jamil Nimeh]

On Thu, 21 Aug 2025 23:30:08 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%.
>
> Ben Perez has updated the pull request incrementally with one additional commit since the last revision:
> 
>   minor edit

Can you also simplify the line near the end of the method where you're doing:
`c2 = c7 - modulus[2] + (c1 >> BITS_PER_LIMB);` to be `c2 = c7 + (c1 >> BITS_PER_LIMB);`?

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PR Comment: https://git.openjdk.org/jdk/pull/26792#issuecomment-3239343260