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LibJS: Implement GetValueFromBuffer AO closer to spec

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No functional changes intended, just some extra asserts added, and a
whole bunch of spec comments.
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Shannon Booth 2023-06-29 17:52:17 +12:00 committed by Linus Groh
parent b1870bc47b
commit 4186fcab9a
1 changed files with 35 additions and 3 deletions
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38
Userland/Libraries/LibJS/Runtime/ArrayBuffer.h
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@ -147,17 +147,49 @@ static Value raw_bytes_to_numeric(VM& vm, ByteBuffer raw_value, bool is_little_e
}
}
// Implementation for 25.1.2.10 GetValueFromBuffer, used in TypedArray<T>::get_value_from_buffer().
// Implementation for 25.1.2.10 GetValueFromBuffer, used in TypedArray<T>::get_value_from_buffer(), https://tc39.es/ecma262/#sec-getvaluefrombuffer
template<typename T>
ThrowCompletionOr<Value> ArrayBuffer::get_value(size_t byte_index, [[maybe_unused]] bool is_typed_array, Order, bool is_little_endian)
{
auto& vm = this->vm();
// 1. Assert: IsDetachedBuffer(arrayBuffer) is false.
VERIFY(!is_detached());
// 2. Assert: There are sufficient bytes in arrayBuffer starting at byteIndex to represent a value of type.
VERIFY(buffer().bytes().slice(byte_index).size() >= sizeof(T));
// 3. Let block be arrayBuffer.[[ArrayBufferData]].
auto& block = buffer();
// 4. Let elementSize be the Element Size value specified in Table 70 for Element Type type.
auto element_size = sizeof(T);
// FIXME: Check for shared buffer
ByteBuffer raw_value;
auto raw_value = TRY_OR_THROW_OOM(vm, buffer_impl().slice(byte_index, element_size));
// FIXME: 5. If IsSharedArrayBuffer(arrayBuffer) is true, then
if (false) {
// FIXME: a. Let execution be the [[CandidateExecution]] field of the surrounding agent's Agent Record.
// FIXME: b. Let eventsRecord be the Agent Events Record of execution.[[EventsRecords]] whose [[AgentSignifier]] is AgentSignifier().
// FIXME: c. If isTypedArray is true and IsNoTearConfiguration(type, order) is true, let noTear be true; otherwise let noTear be false.
// FIXME: d. Let rawValue be a List of length elementSize whose elements are nondeterministically chosen byte values.
// FIXME: e. NOTE: In implementations, rawValue is the result of a non-atomic or atomic read instruction on the underlying hardware. The nondeterminism is a semantic prescription of the memory model to describe observable behaviour of hardware with weak consistency.
// FIXME: f. Let readEvent be ReadSharedMemory { [[Order]]: order, [[NoTear]]: noTear, [[Block]]: block, [[ByteIndex]]: byteIndex, [[ElementSize]]: elementSize }.
// FIXME: g. Append readEvent to eventsRecord.[[EventList]].
// FIXME: h. Append Chosen Value Record { [[Event]]: readEvent, [[ChosenValue]]: rawValue } to execution.[[ChosenValues]].
}
// 6. Else,
else {
// a. Let rawValue be a List whose elements are bytes from block at indices in the interval from byteIndex (inclusive) to byteIndex + elementSize (exclusive).
raw_value = TRY_OR_THROW_OOM(vm, block.slice(byte_index, element_size));
}
// 7. Assert: The number of elements in rawValue is elementSize.
VERIFY(raw_value.size() == element_size);
// 8. If isLittleEndian is not present, set isLittleEndian to the value of the [[LittleEndian]] field of the surrounding agent's Agent Record.
// NOTE: Done by default parameter at declaration of this function.
// 9. Return RawBytesToNumeric(type, rawValue, isLittleEndian).
return raw_bytes_to_numeric<T>(vm, move(raw_value), is_little_endian);
}