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LibJS: Pre-allocate the resolved rope string's underlying buffer

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For performance, rather than slowly incrementing the capacity of the
rope string's buffer, compute an approximate length for that buffer to
be reserved up front.
This commit is contained in:
Timothy Flynn 2024-07-19 15:46:14 -04:00 committed by Andreas Kling
parent 29879a69a4
commit e8f4ae487d
Notes: github-actions[bot] 2024-07-20 04:46:26 +00:00 
Author: https://github.com/trflynn89 🔰
Commit: https://github.com/LadybirdBrowser/ladybird/commit/e8f4ae487d
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/724
1 changed files with 5 additions and 1 deletions
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6
Userland/Libraries/LibJS/Runtime/PrimitiveString.cpp
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@ -254,6 +254,7 @@ void PrimitiveString::resolve_rope_if_needed(EncodingPreference preference) cons
// This vector will hold all the pieces of the rope that need to be assembled
// into the resolved string.
Vector<PrimitiveString const*> pieces;
size_t approximate_length = 0;
// NOTE: We traverse the rope tree without using recursion, since we'd run out of
// stack space quickly when handling a long sequence of unresolved concatenations.
@ -267,6 +268,9 @@ void PrimitiveString::resolve_rope_if_needed(EncodingPreference preference) cons
stack.append(current->m_lhs);
continue;
}
if (current->has_utf8_string())
approximate_length += current->utf8_string_view().length();
pieces.append(current);
}
@ -286,7 +290,7 @@ void PrimitiveString::resolve_rope_if_needed(EncodingPreference preference) cons
}
// Now that we have all the pieces, we can concatenate them using a StringBuilder.
StringBuilder builder;
StringBuilder builder(approximate_length);
// We keep track of the previous piece in order to handle surrogate pairs spread across two pieces.
PrimitiveString const* previous = nullptr;