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Re: [Public WebGL] NaN handling in Typed Array spec



Why not propose that this change be made at the WebIDL level instead? As you point out this is probably not an observable change for most other users of WebIDL.

-James

On Feb 7, 2011 8:09 PM, "Vladimir Vukicevic" <vladimir@mozilla.com> wrote:
>
> I don't think so; pretty sure we discussed this at Mozilla and decided that there was no issue. Cc'ing Andreas to make sure, though. The only tricky thing is that implementations need to make sure that they can handle various NaNs (including signalling ones) creeping into the rest of the engine.
>
> - Vlad
>
> ----- Original Message -----
>> A bug was recently filed against WebKit's implementation of Typed
>> Arrays (https://bugs.webkit.org/show_bug.cgi?id=53598). The basic
>> issue is that the Web IDL specification defines the bit pattern for
>> the not-a-number (NaN) value. Ordinarily, it is not possible for
>> ECMAScript programs to examine this bit pattern, but with the
>> introduction of the Typed Array specification, it is possible to use a
>> Float32Array to store NaN and then read back the bytes using, for
>> example, a Uint8Array.
>>
>> Some ECMAScript engines use multiple representations for NaN
>> internally, and forcing them to be canonicalized into a single bit
>> pattern would impose a significant performance penalty on all stores
>> into Float32Arrays. It is absolutely essential for WebGL programs that
>> loads from and stores into Float32Arrays remain as performant as
>> possible.
>>
>> I would like to add a small, normative section to the Typed Array
>> specification indicating that the bit pattern for NaN values stored
>> using Float32Array, Float64Array and DataView is not specified, and
>> that implementations may utilize any of the legal NaN bit patterns
>> defined by the IEEE-754 specification. I do not believe that doing so
>> would introduce any significant ambiguity into the spec; this is a
>> small corner case.
>>
>> Are there any comments on this proposal?
>>
>> -Ken
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