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AK: Add a UTF-16 string with optimized short- and ASCII-string storage

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This is a strictly UTF-16 string with some optimizations for ASCII.

* If created from a short UTF-8 or UTF-16 string that is also ASCII,
  then the string is stored in an inlined byte buffer.

* If created with a long UTF-8 or UTF-16 string that is also ASCII,
  then the string is stored in an outlined char buffer.

* If created with a short or long UTF-8 or UTF-16 string that is not
  ASCII, then the string is stored in an outlined char16 buffer.

We do not store short non-ASCII text in the inlined buffer to avoid
confusion with operations such as `length_in_code_units` and
`code_unit_at`. For example, "😀" would be stored as 4 UTF-8 bytes
in short string form. But we still want `length_in_code_units` to
be 2, and `code_unit_at(0)` to be 0xD83D.
This commit is contained in:
Timothy Flynn 2025-06-12 19:29:41 -04:00 • committed by Tim Flynn
commit fe676585f5
Notes: github-actions[bot] 2025-07-18 16:47:31 +00:00
17 changed files with 1527 additions and 44 deletions
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4
AK/StringBuilder.cpp
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@ -249,8 +249,10 @@ ErrorOr<void> StringBuilder::try_append(Utf16View const& utf16_view)
{
if (utf16_view.is_empty())
return {};
if (utf16_view.has_ascii_storage())
return try_append(utf16_view.bytes());
auto remaining_view = utf16_view.span();
auto remaining_view = utf16_view.utf16_span();
auto maximum_utf8_length = UnicodeUtils::maximum_utf8_length_from_utf16(remaining_view);
// Possibly over-allocate a little to ensure we don't have to allocate later.