Title: [293807] trunk/Source/WTF/wtf/text/StringView.cpp
- Revision
- 293807
- Author
- cdu...@apple.com
- Date
- 2022-05-04 17:44:40 -0700 (Wed, 04 May 2022)
Log Message
Optimize / simplify slow case in StringView::convertASCIILowercaseAtom() https://bugs.webkit.org/show_bug.cgi?id=240082
Reviewed by Darin Adler.
Optimize / simplify slow case in StringView::convertASCIILowercaseAtom() where the input string
is not already lowercase. We now call `makeAtomString(lowercase(input))` which simplifies the
code a lot and is actually more efficient because makeAtomString() has an optimization that
avoids a StringImpl allocation when the string is relatively small (< 64 characters) and is
already part of the AtomStringTable already.
I validated the implementation by running it in a loop with the String "BODY" and got a
~35% speedup.
* Source/WTF/wtf/text/StringView.cpp:
(WTF::convertASCIILowercaseAtom):
Canonical link: https://commits.webkit.org/250280@main
Modified Paths
Diff
Modified: trunk/Source/WTF/wtf/text/StringView.cpp (293806 => 293807)
--- trunk/Source/WTF/wtf/text/StringView.cpp 2022-05-05 00:20:52 UTC (rev 293806)
+++ trunk/Source/WTF/wtf/text/StringView.cpp 2022-05-05 00:44:40 UTC (rev 293807)
@@ -253,16 +253,8 @@
static AtomString convertASCIILowercaseAtom(const CharacterType* input, unsigned length)
{
for (unsigned i = 0; i < length; ++i) {
- if (UNLIKELY(isASCIIUpper(input[i]))) {
- CharacterType* characters;
- auto result = String::createUninitialized(length, characters);
- StringImpl::copyCharacters(characters, input, i);
- for (; i < length; ++i)
- characters[i] = toASCIILower(input[i]);
- // FIXME: This is inefficient. Ideally, we wouldn't have to allocate a String/StringImpl if the
- // string is already in the AtomStringTable.
- return AtomString(result);
- }
+ if (UNLIKELY(isASCIIUpper(input[i])))
+ return makeAtomString(lowercase(StringView { input, length }));
}
// Fast path when the StringView is already all lowercase.
return AtomString(input, length);
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