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LibJS: Add ASCII fast path to Lexer::current_code_point()

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If the current character under the lexer cursor is ASCII, we don't need
to create a Utf8View to consume a full code point.

This gives a ~3% speedup when parsing the largest Discord JS file.
This commit is contained in:
Andreas Kling 2022-02-13 12:44:57 +01:00
parent c74b6c06a5
commit 3d9f2e2f94
1 changed files with 5 additions and 2 deletions
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7
Userland/Libraries/LibJS/Lexer.cpp
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@ -363,9 +363,12 @@ u32 Lexer::current_code_point() const
static constexpr const u32 REPLACEMENT_CHARACTER = 0xFFFD;
if (m_position == 0)
return REPLACEMENT_CHARACTER;
Utf8View utf_8_view { m_source.substring_view(m_position - 1) };
if (utf_8_view.is_empty())
auto substring = m_source.substring_view(m_position - 1);
if (substring.is_empty())
return REPLACEMENT_CHARACTER;
if (is_ascii(substring[0]))
return substring[0];
Utf8View utf_8_view { substring };
return *utf_8_view.begin();
}