On Sun, 11 Oct 2026 19:17:30 GMT, Liam Miller-Cushon <[email protected]> wrote:
>> This change adds Vector API methods that load the code units of a >> `java.lang.String` into a vector without copying, to allow processing a >> `String` with a vector loop instead of a scalar loop over `charAt`. >> >> As discussed in the [panama-dev@ thread 'String processing and Vector >> APIs'](https://mail.openjdk.org/archives/list/[email protected]/thread/YSPX3TBXZTZEFZNXWDYOZCWLUQPC62P6/), >> one motivating use-case is a regex library that wants to accelerate scans >> for character classes. Implementing these methods outside the JDK using >> scalar `charAt` loops is slower than a vectorized implementation. >> >> ### Goals >> >> * Performance - to get the full performance benefit, these APIs should avoid >> copies or re-encoding, since a copy or re-encoding would be O(n) and reduce >> the performance benefit of a vector loop >> * Encapsulation - encapsulation of `java.lang.String` internals must be >> preserved, including preventing modification of the String's backing >> storage, and also preserving encapsulation of String implementation details >> (like the exact encoding under Compact Strings) >> >> ### Design >> >> >> // ByteVector >> static boolean compatibleWith(String string, Charset charset) >> static ByteVector fromString(VectorSpecies<Byte> species, String string, >> Charset charset, int offset) >> static ByteVector fromString(VectorSpecies<Byte> species, String string, >> Charset charset, int offset, VectorMask<Byte> m) >> >> // ShortVector >> static boolean compatibleWith(String string, Charset charset) >> static ShortVector fromString(VectorSpecies<Short> species, String string, >> Charset charset, int offset) >> static ShortVector fromString(VectorSpecies<Short> species, String string, >> Charset charset, int offset, VectorMask<Short> m) >> >> >> `compatibleWith` runs in constant time. If it returns `true`, `fromString` >> loads the String's backing storage without a copy, if it returns false >> `fromString` will throw `IllegalArgumentException` and callers are expected >> to handle falling back to a scalar loop. >> >> >> if (ByteVector.compatibleWith(s, ISO_8859_1)) { >> // ... >> } else if (ShortVector.compatibleWith(s, UTF_16)) { >> // ... >> } else { >> // scalar fallback >> } >> >> >> These methods deal with strings in terms of code units, not encoded bytes. >> `ShortVector.fromString` loads the String's UTF-16 code units in native byte >> order without a BOM and any unpaired surrogates preserved, providing the >> same values as a scalar loop over `charAt`. Guaranteeing a well-formed >> encoding would... > > Liam Miller-Cushon has updated the pull request with a new target base due to > a merge or a rebase. The incremental webrev excludes the unrelated changes > brought in by the merge/rebase. The pull request contains 13 additional > commits since the last revision: > > - Clean up unused import > - Merge remote-tracking branch 'origin/master' into short-vector > - Move asReadOnlyMemorySegment to String > - Add a benchmark > > Also adjust javadoc, convert test to JUnit 5, other small adjustments > - javadoc > - Move access to jdk.internal.foreign.StringSupport > - Make test inputs longer > - Test coverage > - Move to X-Vector.java.template, update javadoc, add masked overloads > - ShortVector.compatibleWith > - ... and 3 more: https://git.openjdk.org/jdk/compare/dd9f5582...1c6ff6ab src/jdk.incubator.vector/share/classes/jdk/incubator/vector/ByteVector.java line 3809: > 3807: * code units in the specified {@link Charset}} > 3808: * > 3809: * <p>This method runs in constant time, and is intended to be used > as a guard for Perhaps better to separate a bit -- the fact that this runs in constant time seems more of an implNote. But maybe providing an example of how this might be used could help (e.g. show the "if" and then the call) src/jdk.incubator.vector/share/classes/jdk/incubator/vector/ByteVector.java line 3814: > 3812: * @param string the string > 3813: * @param charset the charset representing the 8-bit character > encoding > 3814: * @throws NullPointerException if {@code string} or {@code > charset} is {@code null} Not needed -- the package-info already says that "unless otherwise specified... every method throws NPE" ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/32373#discussion_r4270265735 PR Review Comment: https://git.openjdk.org/jdk/pull/32373#discussion_r4270288943
