On Fri, 17 Apr 2026 07:31:07 GMT, Emanuel Peter <[email protected]> wrote:
>> Found while working on JDK-8369699. >> >> In general, the Vector API documentation is a bit vague around part numbers. >> There was considerable confusion around expansion/contraction: are we >> talking about logical, physical or output expansion/contraction? >> Confusingly, in some places we called expansions things that go from more to >> fewer bits, and we called contractions that went from fewer to more bits. >> >> And exception messages are not very helpful, for example they don't provide >> the legal range. >> >> @rose00 took a first stab at improving things >> (https://github.com/openjdk/jdk/pull/29306), and I eventually took over the >> project. >> >> -------------------------------------- >> >> Principles: >> - Expansion means fewer->more bits. >> - Contraction means more->fewer bits. >> - Be clear about input, logical result and output. >> - We primarily use: >> - conversion lanewise expansion (logical) >> - conversion lanewise contraction (logical) >> - conversion lanewise in-place (logical) >> - reinterpret (logical) >> - select, for truncation (output) >> - insert, for padding (output) >> - in-place, logical fits output (output) >> >> Please review this PR in this order: >> - Changes in the "Expansions, contractions, and partial results" section of >> `Vector.java`. We must first agree on the definitions here, before we go and >> disagree elsewhere ;) >> - Changes in affected methods `convertShape`, `convert`, and >> `reinterpretShape`. >> - Internal changes in `AbstractVector.java`: adjust nomenclature and >> exception message. >> - New test. I think it is necessary, I caught some mistakes I made. And when >> I wanted to add tests for `unslice` I realized that it does not throw for >> out of bounds `part`. So I think it is justified. >> >> In general, I'm a bit worried that the documentation is a bit too long, and >> feels a bit heavy/overwhelming. >> To a large degree, this is due to the complexity of part numbers. >> We could drop some paragraphs and some repetition. Let me know what you >> think is too much. >> More explanations may help make things clearer, but also risk being too much >> and overwhelming. >> I'm open to cut things down more, and any other constructive suggestions ;) >> >> ----------------------- >> >> While reading the documentation and testing for `unslice`, I found out that >> https://github.com/openjdk/jdk/pull/3804 accidentally removed the bounds >> checks for `part`. But we did not notice, because there were no tests for >> it. I'm adding the bounds check back in and adding tests ... > > Emanuel Peter has updated the pull request incrementally with one additional > commit since the last revision: > > after merge with master: fix fuzzer for unslice out of bounds exception Very thorough improvements since I saw this last. The main explanations of expansion/contraction are rephrased and rebalanced well. This is a much more rigorous presentation of "what is going on here", which clarifies the explanation of "why it’s like this". Good tactical repetition around per-method mentions of `Vector.html#expansion`. I like the introduction of the term "exact fit" to amplify the term "in-place". src/jdk.incubator.vector/share/classes/jdk/incubator/vector/Vector.java line 955: > 953: * contracting lane size ({@code ML=1/8}), > 954: * shape-invariant ({@code MP=1}). > 955: * We must insert the logical resut {@code byte[2]:16} into s/resut/result/ These are good examples to prepare the reader for the big table that follows. ------------- Marked as reviewed by jrose (Reviewer). PR Review: https://git.openjdk.org/jdk/pull/30113#pullrequestreview-4174259189 PR Review Comment: https://git.openjdk.org/jdk/pull/30113#discussion_r3140959573
