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Normative: throw whenever creating TA from OOB TA #72

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Dec 21, 2021
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Normative: throw whenever creating TA from OOB TA #72

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Normative: throw whenever creating TA from OOB TA
jugglinmike Aug 26, 2021
b104af7
fixup! Normative: throw whenever creating TA from OOB TA
jugglinmike Nov 4, 2021
433ab77
fixup! Normative: throw whenever creating TA from OOB TA
jugglinmike Nov 5, 2021
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14 changes: 11 additions & 3 deletions spec.html
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Expand Up @@ -758,12 +758,20 @@ <h1>InitializeTypedArrayFromTypedArray ( _O_, _srcArray_ )</h1>
1. Let _bufferConstructor_ be ? SpeciesConstructor(_srcData_, %ArrayBuffer%).
1. Else,
1. Let _bufferConstructor_ be %ArrayBuffer%.
1. <ins>Let _data_ be ? AllocateArrayBuffer(_bufferConstructor_, _byteLength_).</ins>
1. <ins>Let _getSrcBufferByteLength_ be MakeIdempotentArrayBufferByteLengthGetter(~SeqCst~).</ins>
1. <ins>If IsIntegerIndexedObjectOutOfBounds(_srcArray_, _getSrcBufferByteLength_) is *true*, throw a *TypeError* exception.</ins>
1. <ins>Set _elementLength_ to IntegerIndexedObjectLength(_srcArray_, _getSrcBufferByteLength_).</ins>
1. <ins>Set _byteLength_ to _elementSize_ &times; _elementLength_.</ins>
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The new byteLength might be greater than the old byteLength. byteLength should only be updated if the buffer was shrunk. Alternatively, you could assign the new byte length to a newByteLength, and pass min(newByteLength, _byteLength) to CopyDataBlockBytes.

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Persisting the variable _byteLength_ might be confusing in what is becoming a somewhat complicated algorithm (readers might not recognize that despite its authoritative name, its value is not the byte length). There's also _elementLength_ to consider, which maybe ought to be complimented with a corresponding _newElementLength_ (more for coherence than a direct need).

I think we can use the new buffer's [[ArrayBufferByteLength]] slot to get the prior value of _byteLength_ without having to communicate "newness" or "oldness" through variable names. I've pushed up a commit to demonstrate what I have in mind. Does that seem appropriate to you?

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@syg syg Dec 21, 2021 •
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We can't use [[ArrayBufferByteLength]] for growable SharedArrayBuffers, which stores its byte length in a separate shared block. That's why the idempotent getter exists.

I retract my comment, I missed the operative keyword "new". Using the new buffer's [[ArrayBufferByteLength]]. That works for me.

1. If _elementType_ is the same as _srcType_, then
1. Let _data_ be ? CloneArrayBuffer(_srcData_, _srcByteOffset_, _byteLength_, _bufferConstructor_).
1. <del>Let _data_ be ? CloneArrayBuffer(_srcData_, _srcByteOffset_, _byteLength_, _bufferConstructor_).</del>
1. <ins>Let _srcBlock_ be _srcData_.[[ArrayBufferData]].</ins>
1. <ins>Let _targetBlock_ be _data_.[[ArrayBufferData]].</ins>
1. <ins>Let _count_ be min(_byteLength_, _data_.[[ArrayBufferByteLength]]).</ins>
1. <ins>Perform CopyDataBlockBytes(_targetBlock_, 0, _srcBlock_, _srcByteOffset_, _count_).</ins>
1. Else,
1. Let _data_ be ? AllocateArrayBuffer(_bufferConstructor_, _byteLength_).
1. <del>Let _data_ be ? AllocateArrayBuffer(_bufferConstructor_, _byteLength_).</del>
1. <del>If IsDetachedBuffer(_srcData_) is *true*, throw a *TypeError* exception.</del>
1. <ins>If IsIntegerIndexedObjectOutOfBounds(_srcArray_, _getSrcBufferByteLength_) is *true*, throw a *TypeError* exception.</ins>
1. If _srcArray_.[[ContentType]] &ne; _O_.[[ContentType]], throw a *TypeError* exception.
1. Let _srcByteIndex_ be _srcByteOffset_.
1. Let _targetByteIndex_ be 0.
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