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

[Shawn M Emery]

On Wed, 14 Jan 2026 13:27:50 GMT, Ferenc Rakoczi <duke at openjdk.org> wrote:

>> 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.

Ah, I see that now.  Maybe an update to the comments would alleviate my confusion?:
NEW:
    // An intrinsic implementation assumes that the input and output buffers
    // are such that condensed can be read in n-multiples of 192 bytes and
    // parsed can be written in n-multiples of 128 shorts, so callers should allocate
    // the condensed and parsed arrays to at least these amounts, see the assert()

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PR Review Comment: https://git.openjdk.org/jdk/pull/29141#discussion_r2692668352