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LibJS: Fast path for TypedArray.slice()

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We now try to do a bulk memcpy() when possible. This is significantly
faster than going byte-at-a-time.
This commit is contained in:
Andreas Kling 2025-12-01 12:08:11 +01:00 • committed by Jelle Raaijmakers
parent 94fc8c47c0
commit 99bef81d09
Notes: github-actions[bot] 2025-12-01 14:14:00 +00:00
1 changed files with 17 additions and 10 deletions
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27
Libraries/LibJS/Runtime/TypedArrayPrototype.cpp
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@ -1740,19 +1740,26 @@ JS_DEFINE_NATIVE_FUNCTION(TypedArrayPrototype::slice)
return array; return array;
} }
// ix. Repeat, while targetByteIndex < limit, // OPTIMIZATION: If the buffers are not detached and not shared, we can do a single bulk copy.
while (target_byte_index < limit) { if (!target_buffer.is_detached() && !target_buffer.is_shared_array_buffer()
// 1. Let value be GetValueFromBuffer(srcBuffer, srcByteIndex, uint8, true, unordered). && !source_buffer.is_detached() && !source_buffer.is_shared_array_buffer()
auto value = source_buffer.get_value<u8>(source_byte_index.value(), true, ArrayBuffer::Unordered); && &target_buffer.buffer() != &source_buffer.buffer()) {
target_buffer.buffer().overwrite(target_byte_index, source_buffer.buffer().data() + source_byte_index.value(), limit.value() - target_byte_index);
} else {
// ix. Repeat, while targetByteIndex < limit,
while (target_byte_index < limit) {
// 1. Let value be GetValueFromBuffer(srcBuffer, srcByteIndex, uint8, true, unordered).
auto value = source_buffer.get_value<u8>(source_byte_index.value(), true, ArrayBuffer::Unordered);
// 2. Perform SetValueInBuffer(targetBuffer, targetByteIndex, uint8, value, true, unordered). // 2. Perform SetValueInBuffer(targetBuffer, targetByteIndex, uint8, value, true, unordered).
target_buffer.set_value<u8>(target_byte_index, value, true, ArrayBuffer::Unordered); target_buffer.set_value<u8>(target_byte_index, value, true, ArrayBuffer::Unordered);
// 3. Set srcByteIndex to srcByteIndex + 1. // 3. Set srcByteIndex to srcByteIndex + 1.
++source_byte_index; ++source_byte_index;
// 4. Set targetByteIndex to targetByteIndex + 1. // 4. Set targetByteIndex to targetByteIndex + 1.
++target_byte_index; ++target_byte_index;
}
} }
} }
// i. Else, // i. Else,