RFR: 8374755: ML-KEM's 12-bit decompression uses incorrect assertions [v2]

[Ferenc Rakoczi]

On Wed, 14 Jan 2026 06:51:00 GMT, Shawn M Emery <duke at openjdk.org> wrote:

>> Ferenc Rakoczi has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fix off-by-one error discovered by Shawn
>
> src/java.base/share/classes/com/sun/crypto/provider/ML_KEM.java line 1364:
> 
>> 1362:         int n = (parsedLength + 127) / 128;
>> 1363:         assert ((parsed.length >= n * 128) &&
>> 1364:                 (condensed.length >= index + n * 192));
> 
> Given the comments, can this be simplified to just:
> 
> 
> -    int n = (parsedLength + 127) / 128;
> -    assert ((parsed.length >= n * 128) &&
> -                (condensed.length >= index + n * 192));
> +   assert((parsed.length % 128) == 0) && (condensed.length % 192 == 0));
> 
> 
> If the length is smaller than the constant then the remainder will be non-zero.

These are the exact conditions that the most demanding intrinsic (the AVX-512 one) requires. If we would rely on that the callers satisfy these, we wouldn't need the assert :-) . The loop in the intrinsic will read n * 192 bytes and write n * 128 shorts, your suggestion would not ensure that the arrays have at least that much space.

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PR Review Comment: https://git.openjdk.org/jdk/pull/29141#discussion_r2690431489