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<!doctype html>
<meta charset="utf8">
<script src="ecmarkup.js"></script>
<link rel="stylesheet" href="ecmarkup.css">
<title>Resizable ArrayBuffer and growable SharedArrayBuffer</title>
<pre class=metadata>
title: Resizable ArrayBuffer and growable SharedArrayBuffer
status: proposal
stage: 3
location: https://github.com/tc39/proposal-resizablearraybuffer
copyright: false
contributors: Shu-yu Guo
markEffects: true
</pre>
<emu-intro id="intro">
<h1>Resizable ArrayBuffer and growable SharedArrayBuffer</h1>
<p>We extend the `ArrayBuffer` and `SharedArrayBuffer` constructors to take an additional maximum byte length, which would construct dynamically resizable and growable array buffers, respectively.</p>
</emu-intro>
<emu-clause id="sec-arraybuffer-objects-mods">
<h1>Modifications to ArrayBuffer Objects</h1>
<emu-clause id="sec-abstract-operations-for-arraybuffer-objects-mods">
<h1>Modifications to Abstract Operations for ArrayBuffer Objects</h1>
<emu-clause id="sec-detacharraybuffer" type="abstract operation">
<h1>
DetachArrayBuffer (
_arrayBuffer_: an ArrayBuffer,
optional _key_: anything,
): either a normal completion containing ~unused~ or a throw completion
</h1>
<dl class="header">
</dl>
<emu-alg>
1. Assert: IsSharedArrayBuffer(_arrayBuffer_) is *false*.
1. If _key_ is not present, set _key_ to *undefined*.
1. If _arrayBuffer_.[[ArrayBufferDetachKey]] is not _key_, throw a *TypeError* exception.
1. Set _arrayBuffer_.[[ArrayBufferData]] to *null*.
1. Set _arrayBuffer_.[[ArrayBufferByteLength]] to 0.
1. Return ~unused~.
</emu-alg>
<emu-note>
<p>Detaching an ArrayBuffer instance disassociates the Data Block used as its backing store from the instance and sets the byte length of the buffer to 0. <del>No operations defined by this specification use the DetachArrayBuffer abstract operation. However, an ECMAScript host or implementation may define such operations.</del></p>
</emu-note>
</emu-clause>
<emu-clause id="sec-allocatearraybuffer" type="abstract operation">
<h1>
AllocateArrayBuffer (
_constructor_: a constructor,
_byteLength_: a non-negative integer,
<ins>optional _maxByteLength_: a non-negative integer or ~empty~,</ins>
): either a normal completion containing an ArrayBuffer or a throw completion
</h1>
<dl class="header">
<dt>description</dt>
<dd>It is used to create an ArrayBuffer.</dd>
</dl>
<emu-alg>
1. <ins>Let _slots_ be « [[ArrayBufferData]], [[ArrayBufferByteLength]], [[ArrayBufferDetachKey]] ».</ins>
1. <ins>If _maxByteLength_ is present and not ~empty~, then</ins>
1. <ins>If _byteLength_ > _maxByteLength_, throw a *RangeError* exception.</ins>
1. <ins>Append [[ArrayBufferMaxByteLength]] to _slots_.</ins>
1. Let _obj_ be ? OrdinaryCreateFromConstructor(_constructor_, *"%ArrayBuffer.prototype%"*, <del>« [[ArrayBufferData]], [[ArrayBufferByteLength]], [[ArrayBufferDetachKey]] »</del><ins>_slots_</ins>).
1. Let _block_ be ? CreateByteDataBlock(_byteLength_).
1. Set _obj_.[[ArrayBufferData]] to _block_.
1. Set _obj_.[[ArrayBufferByteLength]] to _byteLength_.
1. <ins>If _maxByteLength_ is present and not ~empty~, then</ins>
1. <ins>If it is not possible to create a Data Block _block_ consisting of _maxByteLength_ bytes, throw a *RangeError* exception.</ins>
1. <ins>NOTE: Resizable ArrayBuffers are designed to be implementable with in-place growth. Implementations reserve the right to throw if, for example, virtual memory cannot be reserved up front.</ins>
1. <ins>Set _obj_.[[ArrayBufferMaxByteLength]] to _maxByteLength_.</ins>
1. Return _obj_.
</emu-alg>
</emu-clause>
<ins class="block">
<emu-clause id="sec-arraybufferlength" type="abstract operation">
<h1>
ArrayBufferByteLength (
_arrayBuffer_: an ArrayBuffer or SharedArrayBuffer,
_order_: ~SeqCst~ or ~Unordered~,
): a non-negative integer
</h1>
<dl class="header">
</dl>
<emu-alg>
1. If IsSharedArrayBuffer(_arrayBuffer_) is *true* and _arrayBuffer_ has an [[ArrayBufferByteLengthData]] internal slot, then
1. Let _bufferByteLengthBlock_ be _arrayBuffer_.[[ArrayBufferByteLengthData]].
1. Return ℝ(GetValueFromBuffer(_bufferByteLengthBlock_, 0, ~BigUint64~, *true*, _order_)).
1. Assert: IsDetachedBuffer(_arrayBuffer_) is *false*.
1. Return _arrayBuffer_.[[ArrayBufferByteLength]].
</emu-alg>
</emu-clause>
<emu-clause id="sec-makeidempotentarraybufferbytelengthgetter" type="abstract operation">
<h1>
MakeIdempotentArrayBufferByteLengthGetter (
_order_: ~SeqCst~ or ~Unordered~,
): an Abstract Closure with one parameter
</h1>
<dl class="header">
<dt>description</dt>
<dd>The returned Abstract Closure helps ensure that there there is a single shared memory read event of the byte length data block in the calling operation.</dd>
</dl>
<emu-alg>
1. NOTE: The [[ArrayBuffer]] slot is used for editorial clarity only, that a getter should only be used with a single ArrayBuffer.
1. Let _lengthStorage_ be { [[ArrayBuffer]]: ~empty~, [[ByteLength]]: ~empty~ }.
1. Let _getter_ be a new Abstract Closure with parameters (_buffer_) that captures _lengthStorage_ and _order_ and performs the following steps when called:
1. If _lengthStorage_.[[ByteLength]] is ~empty~, then
1. Assert: _lengthStorage_.[[ArrayBuffer]] is ~empty~.
1. Set _lengthStorage_.[[ArrayBuffer]] to _buffer_.
1. Set _lengthStorage_.[[ByteLength]] to ArrayBufferByteLength(_buffer_, _order_).
1. Assert: SameValue(_lengthStorage_.[[ArrayBuffer]], _buffer_) is *true*.
1. Return _lengthStorage_.[[ByteLength]].
1. Return _getter_.
</emu-alg>
</emu-clause>
<emu-clause id="sec-isresizablearraybuffer" type="abstract operation">
<h1>
IsResizableArrayBuffer (
_arrayBuffer_: an ArrayBuffer or a SharedArrayBuffer,
): a Boolean
</h1>
<dl class="header">
</dl>
<emu-alg>
1. If _arrayBuffer_ has an [[ArrayBufferMaxByteLength]] internal slot, return *true*.
1. Return *false*.
</emu-alg>
</emu-clause>
<emu-clause id="sec-getarraybuffermaxbytelengthoption" type="abstract operation">
<h1>
GetArrayBufferMaxByteLengthOption (
_options_: an ECMAScript language value,
): a normal completion containing either a non-negative integer or ~empty~
</h1>
<dl class="header">
</dl>
<emu-alg>
1. If Type(_options_) is not Object, return ~empty~.
1. Let _maxByteLength_ be ? Get(_options_, `"maxByteLength"`).
1. If _maxByteLength_ is *undefined*, return ~empty~.
1. Return ? ToIndex(_maxByteLength_).
</emu-alg>
</emu-clause>
<emu-clause id="sec-hostresizearraybuffer" type="host-defined abstract operation">
<h1>
HostResizeArrayBuffer (
_buffer_: an ArrayBuffer,
_newByteLength_: a non-negative integer,
): either a normal completion containing either ~handled~ or ~unhandled~, or a throw completion
</h1>
<dl class="header">
<dt>description</dt>
<dd>The host-defined abstract operation HostResizeArrayBuffer takes arguments _buffer_ (an ArrayBuffer object) and _newByteLength_. It gives the host an opportunity to perform implementation-defined resizing of _buffer_. If the host chooses not to handle resizing of _buffer_, it may return ~unhandled~ for the default behaviour.</dd>
</dl>
<p>The implementation of HostResizeArrayBuffer must conform to the following requirements:</p>
<ul>
<li>The abstract operation must return either NormalCompletion(~handled~), NormalCompletion(~unhandled~), or an abrupt throw completion.</li>
<li>The abstract operation does not detach _buffer_.</li>
<li>If the abstract operation completes normally with ~handled~, _buffer_.[[ArrayBufferByteLength]] is _newByteLength_.</li>
</ul>
<p>The default implementation of HostResizeArrayBuffer is to return ~unhandled~.</p>
</emu-clause>
</ins>
</emu-clause>
<emu-clause id="sec-arraybuffer-constructor">
<h1>The ArrayBuffer Constructor</h1>
<emu-clause id="sec-arraybuffer-length">
<h1>ArrayBuffer ( _length_ <ins>[ , _options_ ]</ins> )</h1>
<p>When the `ArrayBuffer` function is called with argument _length_<ins> and optional argument _options_</ins>, the following steps are taken:</p>
<emu-alg>
1. If NewTarget is *undefined*, throw a *TypeError* exception.
1. Let _byteLength_ be ? ToIndex(_length_).
1. <ins>Let _requestedMaxByteLength_ be ? GetArrayBufferMaxByteLengthOption(_options_).</ins>
1. Return ? AllocateArrayBuffer(NewTarget, _byteLength_<ins>, _requestedMaxByteLength_</ins>).
</emu-alg>
</emu-clause>
</emu-clause>
<emu-clause id="sec-properties-of-the-arraybuffer-prototype-object-mods">
<h1>Modifications to the Properties of the ArrayBuffer Prototype Object</h1>
<emu-clause id="sec-get-arraybuffer-@@species">
<h1>get ArrayBuffer [ @@species ]</h1>
<p>`ArrayBuffer[@@species]` is an accessor property whose set accessor function is *undefined*. Its get accessor function performs the following steps:</p>
<emu-alg>
1. Return the *this* value.
</emu-alg>
<p>The value of the *"name"* property of this function is *"get [Symbol.species]"*.</p>
<emu-note>
<p>ArrayBuffer prototype methods normally use their *this* value's constructor to create a derived object. However, a subclass constructor may over-ride that default behaviour <ins>for the <emu-xref href="#sec-arraybuffer.prototype.slice" title></emu-xref> method</ins> by redefining its @@species property.</p>
</emu-note>
</emu-clause>
<ins class="block">
<emu-clause id="sec-get-arraybuffer.prototype.maxbytelength">
<h1>get ArrayBuffer.prototype.maxByteLength</h1>
<p>`ArrayBuffer.prototype.maxByteLength` is an accessor property whose set accessor function is *undefined*. Its get accessor function performs the following steps:</p>
<emu-alg>
1. Let _O_ be the *this* value.
1. Perform ? RequireInternalSlot(_O_, [[ArrayBufferData]]).
1. If IsSharedArrayBuffer(_O_) is *true*, throw a *TypeError* exception.
1. If IsDetachedBuffer(_O_) is *true*, return *+0*<sub>𝔽</sub>.
1. If IsResizableArrayBuffer(_O_) is *true*, then
1. Let _length_ be _O_.[[ArrayBufferMaxByteLength]].
1. Else,
1. Let _length_ be _O_.[[ArrayBufferByteLength]].
1. Return 𝔽(_length_).
</emu-alg>
</emu-clause>
<emu-clause id="sec-get-arraybuffer.prototype.resizable">
<h1>get ArrayBuffer.prototype.resizable</h1>
<p>`ArrayBuffer.prototype.resizable` is an accessor property whose set accessor function is *undefined*. Its get accessor function performs the following steps:</p>
<emu-alg>
1. Let _O_ be the *this* value.
1. Perform ? RequireInternalSlot(_O_, [[ArrayBufferData]]).
1. If IsSharedArrayBuffer(_O_) is *true*, throw a *TypeError* exception.
1. Return IsResizableArrayBuffer(_O_).
</emu-alg>
</emu-clause>
</ins>
<emu-clause id="sec-arraybuffer.prototype.slice">
<h1>ArrayBuffer.prototype.slice ( _start_, _end_ )</h1>
<p>This method performs the following steps when called:</p>
<emu-alg>
1. Let _O_ be the *this* value.
1. Perform ? RequireInternalSlot(_O_, [[ArrayBufferData]]).
1. If IsSharedArrayBuffer(_O_) is *true*, throw a *TypeError* exception.
1. If IsDetachedBuffer(_O_) is *true*, throw a *TypeError* exception.
1. Let _len_ be _O_.[[ArrayBufferByteLength]].
1. Let _relativeStart_ be ? ToIntegerOrInfinity(_start_).
1. If _relativeStart_ is -∞, let _first_ be 0.
1. Else if _relativeStart_ < 0, let _first_ be max(_len_ + _relativeStart_, 0).
1. Else, let _first_ be min(_relativeStart_, _len_).
1. If _end_ is *undefined*, let _relativeEnd_ be _len_; else let _relativeEnd_ be ? ToIntegerOrInfinity(_end_).
1. If _relativeEnd_ is -∞, let _final_ be 0.
1. Else if _relativeEnd_ < 0, let _final_ be max(_len_ + _relativeEnd_, 0).
1. Else, let _final_ be min(_relativeEnd_, _len_).
1. Let _newLen_ be max(_final_ - _first_, 0).
1. Let _ctor_ be ? SpeciesConstructor(_O_, %ArrayBuffer%).
1. Let _new_ be ? Construct(_ctor_, « 𝔽(_newLen_) »).
1. Perform ? RequireInternalSlot(_new_, [[ArrayBufferData]]).
1. If IsSharedArrayBuffer(_new_) is *true*, throw a *TypeError* exception.
1. If IsDetachedBuffer(_new_) is *true*, throw a *TypeError* exception.
1. If SameValue(_new_, _O_) is *true*, throw a *TypeError* exception.
1. If _new_.[[ArrayBufferByteLength]] < _newLen_, throw a *TypeError* exception.
1. NOTE: Side-effects of the above steps may have detached <ins>or resized </ins>_O_.
1. If IsDetachedBuffer(_O_) is *true*, throw a *TypeError* exception.
1. Let _fromBuf_ be _O_.[[ArrayBufferData]].
1. Let _toBuf_ be _new_.[[ArrayBufferData]].
1. <ins>If _first_ < _O_.[[ArrayBufferByteLength]], then</ins>
1. Perform CopyDataBlockBytes(_toBuf_, 0, _fromBuf_, _first_, <ins>min(_O_.[[ArrayBufferByteLength]], </ins>_newLen_<ins>)</ins>).
1. Return _new_.
</emu-alg>
</emu-clause>
<ins class="block">
<emu-clause id="sec-arraybuffer.prototype.resize">
<h1>ArrayBuffer.prototype.resize ( _newLength_ )</h1>
<p>The following steps are taken:</p>
<emu-alg>
1. Let _O_ be the *this* value.
1. Perform ? RequireInternalSlot(_O_, [[ArrayBufferMaxByteLength]]).
1. If IsSharedArrayBuffer(_O_) is *true*, throw a *TypeError* exception.
1. If IsDetachedBuffer(_O_) is *true*, throw a *TypeError* exception.
1. Let _newByteLength_ be ? ToIntegerOrInfinity(_newLength_).
1. If _newByteLength_ < 0 or _newByteLength_ > _O_.[[ArrayBufferMaxByteLength]], throw a *RangeError* exception.
1. Let _hostHandled_ be ? HostResizeArrayBuffer(_O_, _newByteLength_).
1. If _hostHandled_ is ~handled~, return *undefined*.
1. Let _oldBlock_ be _O_.[[ArrayBufferData]].
1. Let _newBlock_ be ? CreateByteDataBlock(_newByteLength_).
1. Let _copyLength_ be min(_newByteLength_, _O_.[[ArrayBufferByteLength]]).
1. Perform CopyDataBlockBytes(_newBlock_, 0, _oldBlock_, 0, _copyLength_).
1. NOTE: Neither creation of the new Data Block nor copying from the old Data Block are observable. Implementations reserve the right to implement this method as in-place growth or shrinkage.
1. Set _O_.[[ArrayBufferData]] to _newBlock_.
1. Set _O_.[[ArrayBufferByteLength]] to _newLength_.
1. Return *undefined*.
</emu-alg>
</emu-clause>
</ins>
</emu-clause>
</emu-clause>
<emu-clause id="sec-sharedarraybuffer-objects-mods">
<h1>Modifications to SharedArrayBuffer Objects</h1>
<emu-clause id="sec-abstract-operations-for-sharedarraybuffer-objects-mods">
<h1>Modifications to Abstract Operations for SharedArrayBuffer Objects</h1>
<emu-clause id="sec-allocatesharedarraybuffer" type="abstract operation">
<h1>
AllocateSharedArrayBuffer (
_constructor_: a constructor,
_byteLength_: a non-negative integer,
<ins>optional _maxByteLength_: a non-negative integer or ~empty~,</ins>
): either a normal completion containing a SharedArrayBuffer or a throw completion
</h1>
<dl class="header">
<dt>description</dt>
<dd>It is used to create a SharedArrayBuffer.</dd>
</dl>
<emu-alg>
1. <ins>Let _slots_ be « [[ArrayBufferData]] ».</ins>
1. <ins>If _maxByteLength_ is present and not ~empty~, then</ins>
1. <ins>If _byteLength_ > _maxByteLength_, throw a *RangeError* exception.</ins>
1. <ins>Append [[ArrayBufferByteLengthData]] and [[ArrayBufferMaxByteLength]] to _slots_.</ins>
1. <ins>Else, append [[ArrayBufferByteLength]] to _slots_.</ins>
1. Let _obj_ be ? OrdinaryCreateFromConstructor(_constructor_, *"%SharedArrayBuffer.prototype%"*, <del>« [[ArrayBufferData]], [[ArrayBufferByteLength]] »</del><ins>_slots_</ins>).
1. <ins>If _maxByteLength_ is present, let _allocLength_ be _maxByteLength_.</ins>
1. <ins>Else, let _allocLength_ be _byteLength_.</ins>
1. Let _block_ be ? CreateSharedByteDataBlock(<del>_byteLength_</del><ins>_allocLength_</ins>).
1. <ins>NOTE: Growable SharedArrayBuffers must be implemented as in-place growable. Creation of a _maxByteLength_ sized Data Block is a specification mechanism. It may be implemented as committing a _byteLength_ sized buffer while reserving _maxByteLength_ in virtual memory.</ins>
1. Set _obj_.[[ArrayBufferData]] to _block_.
1. <ins>If _maxByteLength_ is present and not ~empty~, then</ins>
1. <ins>Assert: _byteLength_ ≤ _maxByteLength_.</ins>
1. <ins>Let _byteLengthBlock_ be ? CreateSharedByteDataBlock(8).</ins>
1. <ins>Perform SetValueInBuffer(_byteLengthBlock_, 0, ~BigUint64~, ℤ(_byteLength_), *true*, ~SeqCst~).</ins>
1. <ins>Set _obj_.[[ArrayBufferByteLengthData]] to _byteLengthBlock_.</ins>
1. <ins>Set _obj_.[[ArrayBufferMaxByteLength]] to _maxByteLength_.</ins>
1. <ins>Else,</ins>
1. Set _obj_.[[ArrayBufferByteLength]] to _byteLength_.
1. Return _obj_.
</emu-alg>
</emu-clause>
<ins class="block">
<emu-clause id="sec-hostgrowsharedarraybuffer" type="host-defined abstract operation">
<h1>
HostGrowSharedArrayBuffer (
_buffer_: a SharedArrayBuffer,
_newByteLength_: a non-negative integer
): either a normal completion containing either ~handled~ or ~unhandled~, or a throw completion
</h1>
<dl class="header">
<dt>description</dt>
<dd>It gives the host an opportunity to perform implementation-defined growing of _buffer_. If the host chooses not to handle resizing of _buffer_, it may return ~unhandled~ for the default behaviour.</dd>
</dl>
<p>The implementation of HostGrowSharedArrayBuffer must conform to the following requirements:</p>
<ul>
<li>The abstract operation must return either NormalCompletion(~handled~), NormalCompletion(~unhandled~), or an abrupt throw completion.</li>
<li>If the abstract operation does not complete normally with ~unhandled~, and _newByteLength_ < the current byte length of the _buffer_ or _newByteLength_ > _buffer_.[[ArrayBufferMaxByteLength]], throw a *RangeError* exception.</li>
<li>Let _isLittleEndian_ be the value of the [[LittleEndian]] field of the surrounding agent's Agent Record. If the abstract operation completes normally with ~handled~, a WriteSharedMemory or ReadModifyWriteSharedMemory event whose [[Order]] is ~SeqCst~, [[Payload]] is NumericToRawBytes(~BigUint64~, _newByteLength_, _isLittleEndian_), [[Block]] is _buffer_.[[ArrayBufferByteLengthData]], [[ByteIndex]] is 0, and [[ElementSize]] is 8 is added to the surrounding agent's candidate execution such that racing calls to `SharedArrayBuffer.prototype.grow` are not "lost", i.e. silently do nothing.</li>
</ul>
<p>The default implementation of HostGrowSharedArrayBuffer is to return ~unhandled~.</p>
<emu-note>
<p>The second requirement above is intentionally vague about how or when the current byte length of _buffer_ is read. Because the byte length must be updated via an atomic read-modify-write operation on the underlying hardware, architectures that use load-link/store-conditional or load-exclusive/store-exclusive instruction pairs may wish to keep the paired instructions close in the instruction stream. As such, SharedArrayBuffer.prototype.grow itself does not perform bounds checking on _newByteLength_ before calling HostGrowSharedArrayBuffer, nor is there a requirement on when the current byte length is read.</p>
<p>This is in contrast with HostResizeArrayBuffer, which is guaranteed that the value of _newByteLength_ is ≥ 0 and ≤ _buffer_.[[ArrayBufferMaxByteLength]].</p>
</emu-note>
</emu-clause>
</ins>
</emu-clause>
<emu-clause id="sec-sharedarraybuffer-constructor">
<h1>The SharedArrayBuffer Constructor</h1>
<emu-clause id="sec-sharedarraybuffer-length">
<h1>SharedArrayBuffer ( _length_ <ins>[ , _options_ ]</ins> )</h1>
<p>When the `SharedArrayBuffer` function is called with argument _length_<ins> and optional argument _options_</ins>, the following steps are taken:</p>
<emu-alg>
1. If NewTarget is *undefined*, throw a *TypeError* exception.
1. Let _byteLength_ be ? ToIndex(_length_).
1. <ins>Let _requestedMaxByteLength_ be ? GetArrayBufferMaxByteLengthOption(_options_).</ins>
1. Return ? AllocateSharedArrayBuffer(NewTarget, _byteLength_<ins>, _requestedMaxByteLength_</ins>).
</emu-alg>
</emu-clause>
</emu-clause>
<emu-clause id="sec-properties-of-the-sharedarraybuffer-prototype-object-mods">
<h1>Modifications to the Properties of the SharedArrayBuffer Prototype Object</h1>
<emu-clause id="sec-get-sharedarraybuffer.prototype.bytelength">
<h1>get SharedArrayBuffer.prototype.byteLength</h1>
<p>`SharedArrayBuffer.prototype.byteLength` is an accessor property whose set accessor function is *undefined*. Its get accessor function performs the following steps:</p>
<emu-alg>
1. Let _O_ be the *this* value.
1. Perform ? RequireInternalSlot(_O_, [[ArrayBufferData]]).
1. If IsSharedArrayBuffer(_O_) is *false*, throw a *TypeError* exception.
1. Let _length_ be <del>_O_.[[ArrayBufferByteLength]]</del><ins>ArrayBufferByteLength(_O_, ~SeqCst~)</ins>.
1. Return 𝔽(_length_).
</emu-alg>
</emu-clause>
<ins class="block">
<emu-clause id="sec-get-sharedarraybuffer.prototype.growable">
<h1>get SharedArrayBuffer.prototype.growable</h1>
<p>`SharedArrayBuffer.prototype.growable` is an accessor property whose set accessor function is *undefined*. Its get accessor function performs the following steps:</p>
<emu-alg>
1. Let _O_ be the *this* value.
1. Perform ? RequireInternalSlot(_O_, [[ArrayBufferData]]).
1. If IsSharedArrayBuffer(_O_) is *false*, throw a *TypeError* exception.
1. Return IsResizableArrayBuffer(_O_).
</emu-alg>
</emu-clause>
<emu-clause id="sec-get-sharedarraybuffer.prototype.maxbytelength">
<h1>get SharedArrayBuffer.prototype.maxByteLength</h1>
<p>`SharedArrayBuffer.prototype.maxByteLength` is an accessor property whose set accessor function is *undefined*. Its get accessor function performs the following steps:</p>
<emu-alg>
1. Let _O_ be the *this* value.
1. Perform ? RequireInternalSlot(_O_, [[ArrayBufferData]]).
1. If IsSharedArrayBuffer(_O_) is *false*, throw a *TypeError* exception.
1. If IsResizableArrayBuffer(_O_) is *true*, then
1. Let _length_ be _O_.[[ArrayBufferMaxByteLength]].
1. Else,
1. Let _length_ be _O_.[[ArrayBufferByteLength]].
1. Return 𝔽(_length_).
</emu-alg>
</emu-clause>
<emu-clause id="sec-sharedarraybuffer.prototype.grow">
<h1>SharedArrayBuffer.prototype.grow ( _newLength_ )</h1>
<p>The following steps are taken:</p>
<emu-alg>
1. Let _O_ be the *this* value.
1. Perform ? RequireInternalSlot(_O_, [[ArrayBufferMaxByteLength]]).
1. If IsSharedArrayBuffer(_O_) is *false*, throw a *TypeError* exception.
1. Let _newByteLength_ be ? ToIntegerOrInfinity(_newLength_).
1. Let _hostHandled_ be ? HostGrowSharedArrayBuffer(_O_, _newByteLength_).
1. If _hostHandled_ is ~handled~, return *undefined*.
1. Let _rawCurrentByteLengthBytesRead_ be a List of length 8 whose elements are nondeterministically chosen byte values.
1. NOTE: In implementations, _rawCurrentByteLengthBytesRead_ is the result of a load-link, of a load-exclusive, or of an operand of a read-modify-write instruction on the underlying hardware. The nondeterminism is a semantic prescription of the memory model to describe observable behaviour of hardware with weak consistency.
1. Let _byteLengthBlock_ be _O_.[[ArrayBufferByteLengthData]].
1. Let _isLittleEndian_ be the value of the [[LittleEndian]] field of the surrounding agent's Agent Record.
1. Let _currentByteLength_ be RawBytesToNumeric(~BigUint64~, _rawCurrentByteLengthBytesRead_, _isLittleEndian_).
1. Let _growFailed_ be *false*.
1. If _newByteLength_ < _currentByteLength_ or _newByteLength_ > _O_.[[ArrayBufferMaxByteLength]], set _growFailed_ to *true*.
1. Let _byteLengthDelta_ be _newByteLength_ - _currentByteLength_.
1. If it is impossible to create a new Shared Data Block value consisting of _byteLengthDelta_ bytes, set _growFailed_ to *true*.
1. NOTE: No new Shared Data Block is constructed and used here. The observable behaviour of growable SharedArrayBuffers is specified by allocating a max-sized Shared Data Block at construction time, and this step is intended to capture the requirement that implementations that run out of memory must throw a *RangeError*.
1. NOTE: The above checks help ensure that concurrent calls to SharedArrayBuffer.prototype.grow are totally ordered. For example, consider two racing calls: `sab.grow(10)` and `sab.grow(20)`. One of the two calls is guaranteed to win the race. The call to `sab.grow(10)` will never shrink `sab` even if `sab.grow(20)` happened first.
1. If _growFailed_ is *false* and _newByteLength_ ≠ _currentByteLength_, then
1. NOTE: Resizes to the same length explicitly do nothing to avoid gratuitous synchronization.
1. Let _second_ be a new read-modify-write modification function with parameters (_oldBytes_, _newBytes_) that captures nothing and performs the following steps atomically when called:
1. Return _newBytes_.
1. Let _newByteLengthBytes_ be NumericToRawBytes(~BigUint64~, ℤ(_newByteLength_), _isLittleEndian_).
1. Let _event_ be ReadModifyWriteSharedMemory { [[Order]]: ~SeqCst~, [[NoTear]]: *true*, [[Block]]: _byteLengthBlock_, [[ByteIndex]]: 0, [[ElementSize]]: 8, [[Payload]]: _newByteLengthBytes_, [[ModifyOp]]: _second_ }.
1. NOTE: The new memory is already zeroed, as a _O_.[[ArrayBufferMaxByteLength]] sized Data Block is already allocated. This is a specification mechanism; an implementation is not required to reserve _O_.[[ArrayBufferMaxByteLength]] bytes of physical memory.
1. Else,
1. Let _event_ be ReadSharedMemory { [[Order]]: ~SeqCst~, [[NoTear]]: *true*, [[Block]]: _byteLengthBlock_, [[ByteIndex]]: 0, [[ElementSize]]: 8 }.
1. Let _execution_ be the [[CandidateExecution]] field of the surrounding agent's Agent Record.
1. Let _eventList_ be the [[EventList]] field of the element in _execution_.[[EventsRecords]] whose [[AgentSignifier]] is AgentSignifier().
1. Append _event_ to _eventList_.
1. Append Chosen Value Record { [[Event]]: _event_, [[ChosenValue]]: _rawCurrentByteLengthBytesRead_ } to _execution_.[[ChosenValues]].
1. If _growFailed_ is *true*, throw a *RangeError* exception.
1. Return *undefined*.
</emu-alg>
<emu-note>
<p>Spurious failures of the compare-exchange to update the length are prohibited. If the bounds checking for the new length passes and the implementation is not out of memory, a ReadModifyWriteSharedMemory event (i.e. a successful compare-exchange) is always added into the candidate execution.</p>
<p>Many of the above steps are shared with the algorithm steps of Atomics.compareExchange and should be refactored when merged into the full specification.</p>
</emu-note>
</emu-clause>
</ins>
<emu-clause id="sec-sharedarraybuffer.prototype.slice">
<h1>SharedArrayBuffer.prototype.slice ( _start_, _end_ )</h1>
<p>This method performs the following steps when called:</p>
<emu-alg>
1. Let _O_ be the *this* value.
1. Perform ? RequireInternalSlot(_O_, [[ArrayBufferData]]).
1. If IsSharedArrayBuffer(_O_) is *false*, throw a *TypeError* exception.
1. Let _len_ be <del>_O_.[[ArrayBufferByteLength]]</del><ins>ArrayBufferByteLength(_O_, ~SeqCst~)</ins>.
1. Let _relativeStart_ be ? ToIntegerOrInfinity(_start_).
1. If _relativeStart_ is -∞, let _first_ be 0.
1. Else if _relativeStart_ < 0, let _first_ be max(_len_ + _relativeStart_, 0).
1. Else, let _first_ be min(_relativeStart_, _len_).
1. If _end_ is *undefined*, let _relativeEnd_ be _len_; else let _relativeEnd_ be ? ToIntegerOrInfinity(_end_).
1. If _relativeEnd_ is -∞, let _final_ be 0.
1. Else if _relativeEnd_ < 0, let _final_ be max(_len_ + _relativeEnd_, 0).
1. Else, let _final_ be min(_relativeEnd_, _len_).
1. Let _newLen_ be max(_final_ - _first_, 0).
1. Let _ctor_ be ? SpeciesConstructor(_O_, %SharedArrayBuffer%).
1. Let _new_ be ? Construct(_ctor_, « 𝔽(_newLen_) »).
1. Perform ? RequireInternalSlot(_new_, [[ArrayBufferData]]).
1. <ins>NOTE: Unlike ArrayBuffers, SharedArrayBuffers cannot shrink, so the length does not need to be reloaded.</ins>
1. If IsSharedArrayBuffer(_new_) is *false*, throw a *TypeError* exception.
1. If _new_.[[ArrayBufferData]] and _O_.[[ArrayBufferData]] are the same Shared Data Block values, throw a *TypeError* exception.
1. If _new_.[[ArrayBufferByteLength]] < _newLen_, throw a *TypeError* exception.
1. Let _fromBuf_ be _O_.[[ArrayBufferData]].
1. Let _toBuf_ be _new_.[[ArrayBufferData]].
1. Perform CopyDataBlockBytes(_toBuf_, 0, _fromBuf_, _first_, _newLen_).
1. Return _new_.
</emu-alg>
</emu-clause>
</emu-clause>
</emu-clause>
<emu-clause id="sec-integer-indexed-exotic-objects-mods">
<h1>Modifications to Integer-Indexed Exotic Objects</h1>
<emu-clause id="sec-integer-indexed-exotic-objects-ownpropertykeys" type="internal method">
<h1>[[OwnPropertyKeys]] ( ): a normal completion containing a List of property keys</h1>
<dl class="header">
<dt>for</dt>
<dd>an Integer-Indexed exotic object _O_</dd>
</dl>
<emu-alg>
1. Let _keys_ be a new empty List.
1. Assert: _O_ is an Integer-Indexed exotic object.
1. <del>If IsDetachedBuffer(_O_.[[ViewedArrayBuffer]]) is *false*, then</del>
1. <del>For each integer _i_ starting with 0 such that _i_ < _O_.[[ArrayLength]], in ascending order, do</del>
1. <del>Add ! ToString(𝔽(_i_)) as the last element of _keys_.</del>
1. <ins>Let _getBufferByteLength_ be MakeIdempotentArrayBufferByteLengthGetter(~SeqCst~).</ins>
1. <ins>Let _len_ be IntegerIndexedObjectLength(_O_, _getBufferByteLength_).</ins>
1. <ins>If _len_ is not ~out-of-bounds~, then</ins>
1. <ins>For each integer _i_ starting with 0 such that _i_ < _len_, in ascending order, do</ins>
1. <ins>Add ! ToString(𝔽(_i_)) as the last element of _keys_.</ins>
1. For each own property key _P_ of _O_ such that Type(_P_) is String and _P_ is not an integer index, in ascending chronological order of property creation, do
1. Add _P_ as the last element of _keys_.
1. For each own property key _P_ of _O_ such that Type(_P_) is Symbol, in ascending chronological order of property creation, do
1. Add _P_ as the last element of _keys_.
1. Return _keys_.
</emu-alg>
</emu-clause>
<emu-clause id="sec-isvalidintegerindex" type="abstract operation">
<h1>
IsValidIntegerIndex (
_O_: an Integer-Indexed exotic object,
_index_: a Number,
): a Boolean
</h1>
<dl class="header">
</dl>
<emu-alg>
1. <del>If IsDetachedBuffer(_O_.[[ViewedArrayBuffer]]) is *true*, return *false*.</del>
1. If IsIntegralNumber(_index_) is *false*, return *false*.
1. If _index_ is *-0*<sub>𝔽</sub>, return *false*.
1. <ins>Let _getBufferByteLength_ be MakeIdempotentArrayBufferByteLengthGetter(~Unordered~).</ins>
1. <ins>NOTE: Bounds checking is not a synchronizing operation when _O_'s backing buffer is a growable SharedArrayBuffer.</ins>
1. <ins>Let _length_ be IntegerIndexedObjectLength(_O_, _getBufferByteLength_).</ins>
1. If <ins>_length_ is ~out-of-bounds~ or</ins> ℝ(_index_) < 0 or ℝ(_index_) ≥ <del>_O_.[[ArrayLength]]</del><ins>_length_</ins>, return *false*.
1. Return *true*.
</emu-alg>
</emu-clause>
<ins class="block">
<emu-clause id="sec-integerindexedobjectbytelength" type="abstract operation">
<h1>
IntegerIndexedObjectByteLength (
_O_: an Integer-Indexed exotic object,
_getBufferByteLength_: an Abstract Closure,
): a non-negative integer
</h1>
<dl class="header">
</dl>
<emu-alg>
1. Let _length_ be IntegerIndexedObjectLength(_O_, _getBufferByteLength_).
1. If _length_ is ~out-of-bounds~ or _length_ = 0, return 0.
1. If _O_.[[ByteLength]] is not ~auto~, return _O_.[[ByteLength]].
1. Let _elementSize_ be TypedArrayElementSize(_O_).
1. Return _length_ × _elementSize_.
</emu-alg>
</emu-clause>
<emu-clause id="sec-integerindexedobjectlength" type="abstract operation">
<h1>
IntegerIndexedObjectLength (
_O_: an Integer-Indexed exotic object,
_getBufferByteLength_: an Abstract Closure,
): a non-negative integer or ~out-of-bounds~
</h1>
<dl class="header">
</dl>
<emu-alg>
1. If IsIntegerIndexedObjectOutOfBounds(_O_, _getBufferByteLength_) is *true*, return ~out-of-bounds~.
1. If _O_.[[ArrayLength]] is not ~auto~, return _O_.[[ArrayLength]].
1. Let _buffer_ be _O_.[[ViewedArrayBuffer]].
1. Let _bufferByteLength_ be _getBufferByteLength_(_buffer_).
1. Assert: IsResizableArrayBuffer(_buffer_) is *true*.
1. Let _byteOffset_ be _O_.[[ByteOffset]].
1. Let _elementSize_ be TypedArrayElementSize(_O_).
1. Return floor((_bufferByteLength_ - _byteOffset_) / _elementSize_).
</emu-alg>
</emu-clause>
<emu-clause id="sec-isintegerindexedobjectoutofbounds" type="abstract operation">
<h1>
IsIntegerIndexedObjectOutOfBounds (
_O_: an Integer-Indexed exotic object,
_getBufferByteLength_: an Abstract Closure,
): a Boolean
</h1>
<dl class="header">
<dt>description</dt>
<dd>It checks if any of the object's numeric properties reference a value at an index not contained within the underlying data block's bounds.</dd>
</dl>
<emu-alg>
1. Let _buffer_ be _O_.[[ViewedArrayBuffer]].
1. If IsDetachedBuffer(_O_.[[ViewedArrayBuffer]]) is *true*, return *true*.
1. Let _bufferByteLength_ be _getBufferByteLength_(_buffer_).
1. Let _byteOffsetStart_ be _O_.[[ByteOffset]].
1. If _O_.[[ArrayLength]] is ~auto~, then
1. Let _byteOffsetEnd_ be _bufferByteLength_.
1. Else,
1. Let _elementSize_ be TypedArrayElementSize(_O_).
1. Let _byteOffsetEnd_ be _byteOffsetStart_ + _O_.[[ArrayLength]] × _elementSize_.
1. If _byteOffsetStart_ > _bufferByteLength_ or _byteOffsetEnd_ > _bufferByteLength_, return *true*.
1. NOTE: 0-length TypedArrays are not considered out-of-bounds.
1. Return *false*.
</emu-alg>
</emu-clause>
<emu-clause id="sec-isarraybufferviewoutofbounds" type="abstract operation">
<h1>
IsArrayBufferViewOutOfBounds(
_O_: an Integer-Indexed exotic object or a DataView,
): a Boolean
</h1>
<dl class="header">
<dt>description</dt>
<dd>It checks if either any of a TypedArray's numeric properties or a DataView object's methods can reference a value at an index not contained within the underlying data block's bounds. This abstract operation exists as a convenience for upstream specifications.</dd>
</dl>
<emu-alg>
1. Let _buffer_ be _O_.[[ViewedArrayBuffer]].
1. If IsDetachedBuffer(_buffer_) is *true*, return *true*.
1. Let _getBufferByteLength_ be MakeIdempotentArrayBufferByteLengthGetter(~SeqCst~).
1. If IsSharedArrayBuffer(_buffer_) is *true*, then
1. Assert: If _O_ has a [[DataView]] internal slot, IsViewOutOfBounds(_O_, _getBufferByteLength_) is *false*. Else, IsIntegerIndexedObjectOutOfBounds(_O_, _getBufferByteLength_) is *false*.
1. NOTE: SharedArrayBuffers can only grow, and views on it cannot go out of bounds after construction. This is special-cased in this operation to avoid shared memory loads of the buffer's byte length, which are not necessary for this check.
1. Return *false*.
1. If _O_ has a [[DataView]] internal slot, return IsViewOutOfBounds(_O_, _getBufferByteLength_).
1. Return IsIntegerIndexedObjectOutOfBounds(_O_, _getBufferByteLength_).
</emu-alg>
</emu-clause>
</ins>
</emu-clause>
<emu-clause id="sec-typedarray-objects-mods">
<h1>Modifications to TypedArray Objects</h1>
<emu-clause id="sec-properties-of-the-%typedarrayprototype%-object-mods">
<h1>Modifications to Properties of the %TypedArray.prototype% Object</h1>
<emu-clause id="sec-validatetypedarray" type="abstract operation">
<h1>
ValidateTypedArray (
_O_: an ECMAScript language value,
): either a normal completion containing ~unused~ or a throw completion
</h1>
<dl class="header">
</dl>
<emu-alg>
1. Perform ? RequireInternalSlot(_O_, [[TypedArrayName]]).
1. Assert: _O_ has a [[ViewedArrayBuffer]] internal slot.
1. Let _buffer_ be _O_.[[ViewedArrayBuffer]].
1. <del>If IsDetachedBuffer(_buffer_) is *true*, throw a *TypeError* exception.</del>
1. <ins>Let _getBufferByteLength_ be MakeIdempotentArrayBufferByteLengthGetter(~SeqCst~).</ins>
1. <ins>If IsIntegerIndexedObjectOutOfBounds(_O_, _getBufferByteLength_) is *true*, throw a *TypeError* exception.</ins>
1. Return _buffer_.
</emu-alg>
</emu-clause>
<emu-clause id="sec-get-%typedarray%.prototype.bytelength">
<h1>get %TypedArray%.prototype.byteLength</h1>
<p>%TypedArray%`.prototype.byteLength` is an accessor property whose set accessor function is *undefined*. Its get accessor function performs the following steps:</p>
<emu-alg>
1. Let _O_ be the *this* value.
1. Perform ? RequireInternalSlot(_O_, [[TypedArrayName]]).
1. Assert: _O_ has a [[ViewedArrayBuffer]] internal slot.
1. Let _buffer_ be _O_.[[ViewedArrayBuffer]].
1. <del>If IsDetachedBuffer(_buffer_) is *true*, return *+0*<sub>𝔽</sub></del>.
1. <ins>Let _getBufferByteLength_ be MakeIdempotentArrayBufferByteLengthGetter(~SeqCst~).</ins>
1. Let _size_ be <del>_O_.[[ByteLength]]</del><ins>IntegerIndexedObjectByteLength(_O_, _getBufferByteLength_)</ins>.
1. Return 𝔽(_size_).
</emu-alg>
</emu-clause>
<emu-clause id="sec-get-%typedarray%.prototype.byteoffset">
<h1>get %TypedArray%.prototype.byteOffset</h1>
<p>%TypedArray%`.prototype.byteOffset` is an accessor property whose set accessor function is *undefined*. Its get accessor function performs the following steps:</p>
<emu-alg>
1. Let _O_ be the *this* value.
1. Perform ? RequireInternalSlot(_O_, [[TypedArrayName]]).
1. Assert: _O_ has a [[ViewedArrayBuffer]] internal slot.
1. Let _buffer_ be _O_.[[ViewedArrayBuffer]].
1. <del>If IsDetachedBuffer(_buffer_) is *true*, return *+0*<sub>𝔽</sub>.</del>
1. <ins>Let _getBufferByteLength_ be MakeIdempotentArrayBufferByteLengthGetter(~SeqCst~).</ins>
1. <ins>If IsIntegerIndexedObjectOutOfBounds(_O_, _getBufferByteLength_) is *true*, return *+0*<sub>𝔽</sub>.</ins>
1. Let _offset_ be _O_.[[ByteOffset]].
1. Return 𝔽(_offset_).
</emu-alg>
</emu-clause>
<emu-clause id="sec-get-%typedarray%.prototype.length">
<h1>get %TypedArray%.prototype.length</h1>
<p>%TypedArray%`.prototype.length` is an accessor property whose set accessor function is *undefined*. Its get accessor function performs the following steps:</p>
<emu-alg>
1. Let _O_ be the *this* value.
1. Perform ? RequireInternalSlot(_O_, [[TypedArrayName]]).
1. Assert: _O_ has [[ViewedArrayBuffer]] and [[ArrayLength]] internal slots.
1. Let _buffer_ be _O_.[[ViewedArrayBuffer]].
1. <del>If IsDetachedBuffer(_buffer_) is *true*, return *+0*<sub>𝔽</sub>.</del>
1. <ins>Let _getBufferByteLength_ be MakeIdempotentArrayBufferByteLengthGetter(~SeqCst~).</ins>
1. Let _length_ be <del>_O_.[[ArrayLength]]</del><ins>IntegerIndexedObjectLength(_O_, _getBufferByteLength_)</ins>.
1. <ins>If _length_ is ~out-of-bounds~, set _length_ to 0.</ins>
1. Return 𝔽(_length_).
</emu-alg>
<p>This function is not generic. The *this* value must be an object with a [[TypedArrayName]] internal slot.</p>
</emu-clause>
<emu-clause id="sec-%typedarray%.prototype.copywithin">
<h1>%TypedArray%.prototype.copyWithin ( _target_, _start_ [ , _end_ ] )</h1>
<p>The interpretation and use of the arguments of %TypedArray%`.prototype.copyWithin` are the same as for `Array.prototype.copyWithin` as defined in <emu-xref href="#sec-array.prototype.copywithin"></emu-xref>.</p>
<p>This method performs the following steps when called:</p>
<emu-alg>
1. Let _O_ be the *this* value.
1. Perform ? ValidateTypedArray(_O_).
1. <ins>Let _getBufferByteLength_ be MakeIdempotentArrayBufferByteLengthGetter(~SeqCst~).</ins>
1. Let _len_ be <del>_O_.[[ArrayLength]]</del><ins>IntegerIndexedObjectLength(_O_, _getBufferByteLength_)</ins>.
1. <ins>Assert: _len_ is not ~out-of-bounds~.</ins>
1. Let _relativeTarget_ be ? ToIntegerOrInfinity(_target_).
1. If _relativeTarget_ is -∞, let _to_ be 0.
1. Else if _relativeTarget_ < 0, let _to_ be max(_len_ + _relativeTarget_, 0).
1. Else, let _to_ be min(_relativeTarget_, _len_).
1. Let _relativeStart_ be ? ToIntegerOrInfinity(_start_).
1. If _relativeStart_ is -∞, let _from_ be 0.
1. Else if _relativeStart_ < 0, let _from_ be max(_len_ + _relativeStart_, 0).
1. Else, let _from_ be min(_relativeStart_, _len_).
1. If _end_ is *undefined*, let _relativeEnd_ be _len_; else let _relativeEnd_ be ? ToIntegerOrInfinity(_end_).
1. If _relativeEnd_ is -∞, let _final_ be 0.
1. Else if _relativeEnd_ < 0, let _final_ be max(_len_ + _relativeEnd_, 0).
1. Else, let _final_ be min(_relativeEnd_, _len_).
1. Let _count_ be min(_final_ - _from_, _len_ - _to_).
1. If _count_ > 0, then
1. NOTE: The copying must be performed in a manner that preserves the bit-level encoding of the source data.
1. Let _buffer_ be _O_.[[ViewedArrayBuffer]].
1. <ins>Set _getBufferByteLength_ to MakeIdempotentArrayBufferByteLengthGetter(~SeqCst~).</ins>
1. <ins>Set _len_ to IntegerIndexedObjectLength(_O_, _getBufferByteLength_).</ins>
1. If <del>IsDetachedBuffer(_buffer_) is *true*</del><ins>_len_ is ~out-of-bounds~</ins>, throw a *TypeError* exception.
1. Let _typedArrayName_ be the String value of _O_.[[TypedArrayName]].
1. Let _elementSize_ be the Element Size value specified in <emu-xref href="#table-the-typedarray-constructors"></emu-xref> for _typedArrayName_.
1. Let _byteOffset_ be _O_.[[ByteOffset]].
1. <ins>Let _bufferByteLimit_ be _len_ × _elementSize_ + _byteOffset_.</ins>
1. Let _toByteIndex_ be _to_ × _elementSize_ + _byteOffset_.
1. Let _fromByteIndex_ be _from_ × _elementSize_ + _byteOffset_.
1. Let _countBytes_ be _count_ × _elementSize_.
1. If _fromByteIndex_ < _toByteIndex_ and _toByteIndex_ < _fromByteIndex_ + _countBytes_, then
1. Let _direction_ be -1.
1. Set _fromByteIndex_ to _fromByteIndex_ + _countBytes_ - 1.
1. Set _toByteIndex_ to _toByteIndex_ + _countBytes_ - 1.
1. Else,
1. Let _direction_ be 1.
1. Repeat, while _countBytes_ > 0,
1. <ins>If _fromByteIndex_ < _bufferByteLimit_ and _toByteIndex_ < _bufferByteLimit_, then</ins>
1. Let _value_ be GetValueFromBuffer(_buffer_, _fromByteIndex_, ~Uint8~, *true*, ~Unordered~).
1. Perform SetValueInBuffer(_buffer_, _toByteIndex_, ~Uint8~, _value_, *true*, ~Unordered~).
1. Set _fromByteIndex_ to _fromByteIndex_ + _direction_.
1. Set _toByteIndex_ to _toByteIndex_ + _direction_.
1. Set _countBytes_ to _countBytes_ - 1.
1. Return _O_.
</emu-alg>
</emu-clause>
<emu-clause id="sec-%typedarray%.prototype.fill">
<h1>%TypedArray%.prototype.fill ( _value_ [ , _start_ [ , _end_ ] ] )</h1>
<p>The interpretation and use of the arguments of %TypedArray%`.prototype.fill` are the same as for `Array.prototype.fill` as defined in <emu-xref href="#sec-array.prototype.fill"></emu-xref>.</p>
<p>This method performs the following steps when called:</p>
<emu-alg>
1. Let _O_ be the *this* value.
1. Perform ? ValidateTypedArray(_O_).
1. <ins>Let _getBufferByteLength_ be MakeIdempotentArrayBufferByteLengthGetter(~SeqCst~).</ins>
1. Let _len_ be <del>_O_.[[ArrayLength]]</del><ins>IntegerIndexedObjectLength(_O_, _getBufferByteLength_)</ins>.
1. <ins>Assert: _len_ is not ~out-of-bounds~.</ins>
1. If _O_.[[ContentType]] is ~BigInt~, set _value_ to ? ToBigInt(_value_).
1. Otherwise, set _value_ to ? ToNumber(_value_).
1. Let _relativeStart_ be ? ToIntegerOrInfinity(_start_).
1. If _relativeStart_ is -∞, let _k_ be 0.
1. Else if _relativeStart_ < 0, let _k_ be max(_len_ + _relativeStart_, 0).
1. Else, let _k_ be min(_relativeStart_, _len_).
1. If _end_ is *undefined*, let _relativeEnd_ be _len_; else let _relativeEnd_ be ? ToIntegerOrInfinity(_end_).
1. If _relativeEnd_ is -∞, let _final_ be 0.
1. Else if _relativeEnd_ < 0, let _final_ be max(_len_ + _relativeEnd_, 0).
1. Else, let _final_ be min(_relativeEnd_, _len_).
1. <del>If IsDetachedBuffer(_O_.[[ViewedArrayBuffer]]) is *true*, throw a *TypeError* exception.</del>
1. <ins>Set _getBufferByteLength_ to MakeIdempotentArrayBufferByteLengthGetter(~SeqCst~).</ins>
1. <ins>Set _len_ to IntegerIndexedObjectLength(_O_, _getBufferByteLength_).</ins>
1. <ins>If _len_ is ~out-of-bounds~, throw a *TypeError* exception.</ins>
1. <ins>Set _final_ to min(_final_, _len_).</ins>
1. Repeat, while _k_ < _final_,
1. Let _Pk_ be ! ToString(𝔽(_k_)).
1. Perform ! Set(_O_, _Pk_, _value_, *true*).
1. Set _k_ to _k_ + 1.
1. Return _O_.
</emu-alg>
</emu-clause>
<emu-clause id="sec-%typedarray%.prototype.slice">
<h1>%TypedArray%.prototype.slice ( _start_, _end_ )</h1>
<p>The interpretation and use of the arguments of %TypedArray%`.prototype.slice` are the same as for `Array.prototype.slice` as defined in <emu-xref href="#sec-array.prototype.slice"></emu-xref>. The following steps are taken:</p>
<p>This method performs the following steps when called:</p>
<emu-alg>
1. Let _O_ be the *this* value.
1. Perform ? ValidateTypedArray(_O_).
1. <ins>Let _getBufferByteLength_ be MakeIdempotentArrayBufferByteLengthGetter(~SeqCst~).</ins>
1. Let _len_ be <del>_O_.[[ArrayLength]]</del><ins>IntegerIndexedObjectLength(_O_, _getBufferByteLength_)</ins>.
1. <ins>Assert: _len_ is not ~out-of-bounds~.</ins>
1. Let _relativeStart_ be ? ToIntegerOrInfinity(_start_).
1. If _relativeStart_ is -∞, let _k_ be 0.
1. Else if _relativeStart_ < 0, let _k_ be max(_len_ + _relativeStart_, 0).
1. Else, let _k_ be min(_relativeStart_, _len_).
1. If _end_ is *undefined*, let _relativeEnd_ be _len_; else let _relativeEnd_ be ? ToIntegerOrInfinity(_end_).
1. If _relativeEnd_ is -∞, let _final_ be 0.
1. Else if _relativeEnd_ < 0, let _final_ be max(_len_ + _relativeEnd_, 0).
1. Else, let _final_ be min(_relativeEnd_, _len_).
1. Let _count_ be max(_final_ - _k_, 0).
1. Let _A_ be ? TypedArraySpeciesCreate(_O_, « 𝔽(_count_) »).
1. If _count_ > 0, then
1. <del>If IsDetachedBuffer(_O_.[[ViewedArrayBuffer]]) is *true*, throw a *TypeError* exception.</del>
1. <ins>Set _getBufferByteLength_ to MakeIdempotentArrayBufferByteLengthGetter(~SeqCst~).</ins>
1. <ins>Set _len_ to IntegerIndexedObjectLength(_O_, _getBufferByteLength_).</ins>
1. <ins>If _len_ is ~out-of-bounds~, throw a *TypeError* exception.</ins>
1. <ins>Set _final_ to min(_final_, _len_).</ins>
1. Let _srcName_ be the String value of _O_.[[TypedArrayName]].
1. Let _srcType_ be the Element Type value in <emu-xref href="#table-the-typedarray-constructors"></emu-xref> for _srcName_.
1. Let _targetName_ be the String value of _A_.[[TypedArrayName]].
1. Let _targetType_ be the Element Type value in <emu-xref href="#table-the-typedarray-constructors"></emu-xref> for _targetName_.
1. If _srcType_ is different from _targetType_, then
1. Let _n_ be 0.
1. Repeat, while _k_ < _final_,
1. Let _Pk_ be ! ToString(𝔽(_k_)).
1. Let _kValue_ be ! Get(_O_, _Pk_).
1. Perform ! Set(_A_, ! ToString(𝔽(_n_)), _kValue_, *true*).
1. Set _k_ to _k_ + 1.
1. Set _n_ to _n_ + 1.
1. Else,
1. Let _srcBuffer_ be _O_.[[ViewedArrayBuffer]].
1. Let _targetBuffer_ be _A_.[[ViewedArrayBuffer]].
1. Let _elementSize_ be the Element Size value specified in <emu-xref href="#table-the-typedarray-constructors"></emu-xref> for Element Type _srcType_.
1. NOTE: If _srcType_ and _targetType_ are the same, the transfer must be performed in a manner that preserves the bit-level encoding of the source data.
1. Let _srcByteOffset_ be _O_.[[ByteOffset]].
1. Let _targetByteIndex_ be _A_.[[ByteOffset]].
1. Let _srcByteIndex_ be (_k_ × _elementSize_) + _srcByteOffset_.
1. Let _limit_ be _targetByteIndex_ + <ins>min(</ins>_count_<ins>, _len_)</ins> × _elementSize_.
1. Repeat, while _targetByteIndex_ < _limit_,
1. Let _value_ be GetValueFromBuffer(_srcBuffer_, _srcByteIndex_, ~Uint8~, *true*, ~Unordered~).
1. Perform SetValueInBuffer(_targetBuffer_, _targetByteIndex_, ~Uint8~, _value_, *true*, ~Unordered~).
1. Set _srcByteIndex_ to _srcByteIndex_ + 1.
1. Set _targetByteIndex_ to _targetByteIndex_ + 1.
1. Return _A_.
</emu-alg>
<p>This function is not generic. The *this* value must be an object with a [[TypedArrayName]] internal slot.</p>
</emu-clause>
<emu-clause id="sec-%typedarray%.prototype.subarray">
<h1>%TypedArray%.prototype.subarray ( _begin_, _end_ )</h1>
<p>Returns a new _TypedArray_ whose element type is the same as this _TypedArray_ and whose ArrayBuffer is the same as the ArrayBuffer of this _TypedArray_, referencing the elements at _begin_, inclusive, up to _end_, exclusive. If either _begin_ or _end_ is negative, it refers to an index from the end of the array, as opposed to from the beginning.</p>
<p>This method performs the following steps when called:</p>
<emu-alg>
1. Let _O_ be the *this* value.
1. Perform ? RequireInternalSlot(_O_, [[TypedArrayName]]).
1. Assert: _O_ has a [[ViewedArrayBuffer]] internal slot.
1. Let _buffer_ be _O_.[[ViewedArrayBuffer]].
1. <ins>Let _getSrcBufferByteLength_ be MakeIdempotentArrayBufferByteLengthGetter(~SeqCst~).</ins>
1. Let _srcLength_ be <del>_O_.[[ArrayLength]]</del><ins>IntegerIndexedObjectLength(_O_, _getSrcBufferByteLength_)</ins>.
1. <ins>If _srcLength_ is ~out-of-bounds~, set _srcLength_ to 0.</ins>
1. Let _relativeBegin_ be ? ToIntegerOrInfinity(_begin_).
1. If _relativeBegin_ is -∞, let _beginIndex_ be 0.
1. Else if _relativeBegin_ < 0, let _beginIndex_ be max(_srcLength_ + _relativeBegin_, 0).
1. Else, let _beginIndex_ be min(_relativeBegin_, _srcLength_).
1. <ins>If _O_.[[ArrayLength]] is ~auto~ and _end_ is *undefined*, then</ins>
1. <ins>Let _newLength_ be *undefined*.</ins>
1. <ins>Else,</ins>
1. If _end_ is *undefined*, let _relativeEnd_ be _srcLength_; else let _relativeEnd_ be ? ToIntegerOrInfinity(_end_).
1. If _relativeEnd_ is -∞, let _endIndex_ be 0.
1. Else if _relativeEnd_ < 0, let _endIndex_ be max(_srcLength_ + _relativeEnd_, 0).
1. Else, let _endIndex_ be min(_relativeEnd_, _srcLength_).
1. Let _newLength_ be max(_endIndex_ - _beginIndex_, 0).
1. Let _constructorName_ be the String value of _O_.[[TypedArrayName]].
1. Let _elementSize_ be the Element Size value specified in <emu-xref href="#table-the-typedarray-constructors"></emu-xref> for _constructorName_.
1. Let _srcByteOffset_ be _O_.[[ByteOffset]].
1. Let _beginByteOffset_ be _srcByteOffset_ + _beginIndex_ × _elementSize_.
1. <ins>If _newLength_ is *undefined*, then</ins>
1. <ins>Let _argumentsList_ be « _buffer_, 𝔽(_beginByteOffset_) ».</ins>
1. <ins>Else,</ins>
1. Let _argumentsList_ be « _buffer_, 𝔽(_beginByteOffset_), 𝔽(_newLength_) ».
1. Return ? TypedArraySpeciesCreate(_O_, _argumentsList_).
</emu-alg>
<p>This function is not generic. The *this* value must be an object with a [[TypedArrayName]] internal slot.</p>
</emu-clause>
<emu-clause id="sec-settypedarrayfromtypedarray" type="abstract operation" oldids="sec-%typedarray%.prototype.set-typedarray-offset">
<h1>
SetTypedArrayFromTypedArray (
_target_: a TypedArray,
_targetOffset_: a non-negative integer or +∞,
_source_: a TypedArray,
): either a normal completion containing ~unused~ or a throw completion
</h1>
<dl class="header">
<dt>description</dt>
<dd>It sets multiple values in _target_, starting at index _targetOffset_, reading the values from _source_.</dd>
</dl>
<emu-alg>
1. Assert: _source_ is an Object that has a [[TypedArrayName]] internal slot.
1. Let _targetBuffer_ be _target_.[[ViewedArrayBuffer]].
1. <del>If IsDetachedBuffer(_targetBuffer_) is *true*, throw a *TypeError* exception.</del>
1. <ins>Let _getTargetBufferByteLength_ be MakeIdempotentArrayBufferByteLengthGetter(~SeqCst~).</ins>
1. Let _targetLength_ be <del>_target_.[[ArrayLength]]</del><ins>IntegerIndexedObjectLength(_target_, _getTargetBufferByteLength_)</ins>.
1. <ins>If _targetLength_ is ~out-of-bounds~, throw a *TypeError* exception.</ins>
1. Let _srcBuffer_ be _source_.[[ViewedArrayBuffer]].
1. <del>If IsDetachedBuffer(_srcBuffer_) is *true*, throw a *TypeError* exception.</del>
1. Let _targetType_ be TypedArrayElementType(_target_).
1. Let _targetElementSize_ be TypedArrayElementSize(_target_).
1. Let _targetByteOffset_ be _target_.[[ByteOffset]].
1. Let _srcType_ be TypedArrayElementType(_source_).
1. Let _srcElementSize_ be TypedArrayElementSize(_source_).
1. <ins>Let _getSrcBufferByteLength_ be MakeIdempotentArrayBufferByteLengthGetter(~SeqCst~).</ins>
1. Let _srcLength_ be <del>_source_.[[ArrayLength]]</del><ins>IntegerIndexedObjectLength(_source_, _getSrcBufferByteLength_)</ins>.
1. <ins>If _srcLength_ is ~out-of-bounds~, throw a *TypeError* exception.</ins>
1. Let _srcByteOffset_ be _source_.[[ByteOffset]].
1. If _targetOffset_ is +∞, throw a *RangeError* exception.
1. If _srcLength_ + _targetOffset_ > _targetLength_, throw a *RangeError* exception.
1. If _target_.[[ContentType]] ≠ _source_.[[ContentType]], throw a *TypeError* exception.
1. If both IsSharedArrayBuffer(_srcBuffer_) and IsSharedArrayBuffer(_targetBuffer_) are *true*, then
1. If _srcBuffer_.[[ArrayBufferData]] and _targetBuffer_.[[ArrayBufferData]] are the same Shared Data Block values, let _same_ be *true*; else let _same_ be *false*.
1. Else, let _same_ be SameValue(_srcBuffer_, _targetBuffer_).
1. If _same_ is *true*, then
1. Let _srcByteLength_ be <del>_source_.[[ByteLength]]</del><ins>IntegerIndexedObjectByteLength(_source_, _getSrcBufferByteLength_)</ins>.
1. Set _srcBuffer_ to ? CloneArrayBuffer(_srcBuffer_, _srcByteOffset_, _srcByteLength_).
1. Let _srcByteIndex_ be 0.
1. Else, let _srcByteIndex_ be _srcByteOffset_.
1. Let _targetByteIndex_ be _targetOffset_ × _targetElementSize_ + _targetByteOffset_.
1. Let _limit_ be _targetByteIndex_ + _targetElementSize_ × _srcLength_.
1. If _srcType_ is the same as _targetType_, then
1. NOTE: If _srcType_ and _targetType_ are the same, the transfer must be performed in a manner that preserves the bit-level encoding of the source data.
1. Repeat, while _targetByteIndex_ < _limit_,
1. Let _value_ be GetValueFromBuffer(_srcBuffer_, _srcByteIndex_, ~Uint8~, *true*, ~Unordered~).
1. Perform SetValueInBuffer(_targetBuffer_, _targetByteIndex_, ~Uint8~, _value_, *true*, ~Unordered~).
1. Set _srcByteIndex_ to _srcByteIndex_ + 1.
1. Set _targetByteIndex_ to _targetByteIndex_ + 1.
1. Else,
1. Repeat, while _targetByteIndex_ < _limit_,
1. Let _value_ be GetValueFromBuffer(_srcBuffer_, _srcByteIndex_, _srcType_, *true*, ~Unordered~).
1. Perform SetValueInBuffer(_targetBuffer_, _targetByteIndex_, _targetType_, _value_, *true*, ~Unordered~).
1. Set _srcByteIndex_ to _srcByteIndex_ + _srcElementSize_.
1. Set _targetByteIndex_ to _targetByteIndex_ + _targetElementSize_.
</emu-alg>
</emu-clause>
</emu-clause>
<emu-clause id="sec-typedarray-constructors-mods">
<h1>Modifications to the _TypedArray_ Constructors</h1>
<emu-clause id="sec-initializetypedarrayfromtypedarray" type="abstract operation" oldids="sec-typedarray-typedarray">
<h1>
InitializeTypedArrayFromTypedArray (
_O_: a TypedArray,
_srcArray_: a TypedArray,
): either a normal completion containing ~unused~ or a throw completion
</h1>
<dl class="header">
</dl>
<emu-alg>
1. Let _srcData_ be _srcArray_.[[ViewedArrayBuffer]].
1. <del>If IsDetachedBuffer(_srcData_) is *true*, throw a *TypeError* exception.</del>
1. Let _elementType_ be TypedArrayElementType(_O_).
1. Let _elementSize_ be TypedArrayElementSize(_O_).
1. <ins>Let _getSrcBufferByteLength_ be MakeIdempotentArrayBufferByteLengthGetter(~SeqCst~).</ins>
1. Let _elementLength_ be <del>_srcArray_.[[ArrayLength]]</del><ins>IntegerIndexedObjectLength(_srcArray_, _getSrcBufferByteLength_)</ins>.
1. <ins>If _elementLength_ is ~out-of-bounds~, throw a *TypeError* exception.</ins>
1. Let _srcType_ be TypedArrayElementType(_srcArray_).
1. Let _srcElementSize_ be TypedArrayElementSize(_srcArray_).
1. Let _srcByteOffset_ be _srcArray_.[[ByteOffset]].
1. Let _byteLength_ be _elementSize_ × _elementLength_.
1. If _elementType_ is the same as _srcType_, then
1. Let _data_ be ? CloneArrayBuffer(_srcData_, _srcByteOffset_, _byteLength_).
1. Else,
1. Let _data_ be ? <emu-meta suppress-effects="user-code">AllocateArrayBuffer(%ArrayBuffer%, _byteLength_)</emu-meta>.
1. If _srcArray_.[[ContentType]] ≠ _O_.[[ContentType]], throw a *TypeError* exception.
1. Let _srcByteIndex_ be _srcByteOffset_.
1. Let _targetByteIndex_ be 0.
1. Let _count_ be _elementLength_.
1. Repeat, while _count_ > 0,
1. Let _value_ be GetValueFromBuffer(_srcData_, _srcByteIndex_, _srcType_, *true*, ~Unordered~).
1. Perform SetValueInBuffer(_data_, _targetByteIndex_, _elementType_, _value_, *true*, ~Unordered~).
1. Set _srcByteIndex_ to _srcByteIndex_ + _srcElementSize_.
1. Set _targetByteIndex_ to _targetByteIndex_ + _elementSize_.
1. Set _count_ to _count_ - 1.
1. Set _O_.[[ViewedArrayBuffer]] to _data_.
1. Set _O_.[[ByteLength]] to _byteLength_.
1. Set _O_.[[ByteOffset]] to 0.
1. Set _O_.[[ArrayLength]] to _elementLength_.
1. Return ~unused~.
</emu-alg>
</emu-clause>
<emu-clause id="sec-initializetypedarrayfromarraybuffer" type="abstract operation" oldids="sec-typedarray-buffer-byteoffset-length">