RFR: 8371450: AES performance improvements for key schedule generation

[Shawn M Emery]

On Fri, 7 Nov 2025 10:39:37 GMT, Ferenc Rakoczi <duke at openjdk.org> wrote:

>> This fix improves performance in the AES key schedule generation by eliminating an unnecessary object and unnecessary mask in the inverse key schedule.
>> 
>> The micro:org.openjdk.bench.javax.crypto.AESReinit benchmark results are improved by 6.96% for arm64 and 7.79% for x86_64.
>> 
>> Thank you @jnimeh for catching the unnecessary byte mask!
>
> src/java.base/share/classes/com/sun/crypto/provider/AES_Crypt.java line 1017:
> 
>> 1015:                 | ((SBOX[(b1 & 0xF0) >> 4][b1 & 0x0F] & 0xFF) << 16)
>> 1016:                 | ((SBOX[(b2 & 0xF0) >> 4][b2 & 0x0F] & 0xFF) << 8)
>> 1017:                 | (SBOX[(word & 0xF0) >> 4][word & 0x0F] & 0xFF);
> 
> I think there is no need for any of these bytes. Every index can be computed as "(word >> offset) & 0x0F". Actually, if you define SBOX as a 1-dim array, you can index into it with "(word >> offset) & 0xFF".

Thank you for your review.  The byte assignments were to avoid three redundant shift operations.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28188#discussion_r2505772947