endianness

Brendan Eich brendan at mozilla.com
Tue Mar 26 17:18:19 PDT 2013


Kenneth Russell wrote:
> On Tue, Mar 26, 2013 at 4:35 PM, David Herman<dherman at mozilla.com>  wrote:
>> [breaking out a new thread since this is orthogonal to the NaN issue]
>>
>> While the Khronos spec never specified an endianness, TC39 agreed in May 2012 to make the byte order explicitly little-endian in ES6:
>>
>>      https://mail.mozilla.org/pipermail/es-discuss/2012-May/022834.html
>>
>> The de facto reality is that there are essentially no big-endian browsers for developers to test on. Web content is being invited to introduce byte-order dependencies. DataView is usually held up as the counter-argument, as if the *existence* of a safe alternative API means no one will ever misuse the unsafe one. Even if we don't take into account human nature, Murphy's Law, and the fact that the web is the world's largest fuzz tester, a wholly rational developer may often prefer not to use DataView because it's still easier to read out bytes using [ ] notation instead of DataView methods.
>>
>> I myself -- possibly the one person in the world who cares most about this issue! -- accidentally created a buggy app that wouldn't work on a big-endian system, because I had no way of testing it:
>>
>>      https://github.com/dherman/float.js/commit/deb5bf2f5696ce29d9a6c1a6bf7c479a3784fd7b
>>
>> In summary: we already agreed on TC39 to close this loophole, it's the right thing to do, and concern about potential performance issues on non-existent browsers of non-existent systems should not trump portability and correctly executing existing web content.
>
> I am disappointed that this decision was made without input from both
> of the editors of the typed array spec and disagree with the statement
> that it is the right thing to do.

First, my apologies to Dave for forgetting the May decision. I was 
looking in the wrong place for a record of that decision!

Second, I understand Ken's point of view (old SGI hacker here) but have 
to question it on the grounds Dave raises: no one is testing, so there 
are very likely to be latent little-endian dependencies in deployed code 
today.

So why not codify this? Because it might penalize big-endian systems? 
The IP protocols use big-endian byte order (owing to the pre-Intel 
big-endian architectures of IMPs and early Internet machines) and so 
penalize Intel machines, and we take the hit (and it's small on modern 
super-scalar CPUs).

Ken, a couple of questions:

1. Do you know of any big-endian systems with market share that host JS 
implementations? It would be great to have a list.

2. Independent of the answer to (1), today's web browsers run on 
little-endian systems and that has very likely created a de-facto 
standard. If we codify it, we make the small to empty set of big-endian 
systems pay a price. Why is this the wrong thing for typed arrays but 
the right thing (in reverse! majority-architectures penalized) for the 
IP protocol suite?

/be

>
> -Ken
>
>
>> Dave
>>
>> This was not the plan of record on TC39. The plan was to fix the semantics as little-endian.
>>
>> On Mar 25, 2013, at 6:00 PM, Brendan Eich<brendan at mozilla.com>  wrote:
>>
>>> Right, thanks for the reminder. It all comes back now, including the "how to write correct ending-independent typed array code" bit.
>>>
>>> /be
>>>
>>> On Mar 25, 2013, at 4:33 PM, Kenneth Russell<kbr at google.com>  wrote:
>>>
>>>> On Mon, Mar 25, 2013 at 4:23 PM, Brendan Eich<brendan at mozilla.com>  wrote:
>>>>> Allen Wirfs-Brock wrote:
>>>>>> On Mar 25, 2013, at 4:05 PM, Brendan Eich wrote:
>>>>>>
>>>>>>> Allen Wirfs-Brock wrote:
>>>>>>>> BTW, isn't cannonicalization of endian-ness for both integers and floats
>>>>>>>> a bigger interop issue than NaN cannonicalization?  I know this was
>>>>>>>> discussed in the past, but it doesn't seem to be covered in the latest
>>>>>>>> Khronos spec.  Was there ever a resolution as to whether or not TypedArray
>>>>>>>> [[Set]] operations need to use a cannonical endian-ness?
>>>>>>> Search for "byte order" at
>>>>>>> https://www.khronos.org/registry/typedarray/specs/latest/.
>>>>>> I had already search for "endian" with similar results.  It says that the
>>>>>> default for DataViews gets/sets that do not specify a byte order is
>>>>>> big-endean. It doesn't say anything (that I can find) about such accesses on
>>>>>> TypedArray gets/sets.
>>>>> Oh, odd -- I recall that it used to say little-endian. Typed arrays are LE
>>>>> to match dominant architectures, while DataViews are BE to match packed
>>>>> serialization use-cases.
>>>>>
>>>>> Ken, did something get edited out?
>>>> No. The typed array views (everything except DataView) have used the
>>>> host machine's endianness from day one by design -- although the typed
>>>> array spec does not state this explicitly. If desired, text can be
>>>> added to the specification to this effect. Any change in this behavior
>>>> will destroy the performance of APIs like WebGL and Web Audio on
>>>> big-endian architectures.
>>>>
>>>> Correctly written code works identically on big-endian and
>>>> little-endian architectures. See
>>>> http://www.html5rocks.com/en/tutorials/webgl/typed_arrays/ for a
>>>> detailed description of the usage of the APIs.
>>>>
>>>> DataView, which is designed for input/output, operates on data with a
>>>> specified endianness.
>>>>
>>>> -Ken
>>>> _______________________________________________
>>>> es-discuss mailing list
>>>> es-discuss at mozilla.org
>>>> https://mail.mozilla.org/listinfo/es-discuss
>>> _______________________________________________
>>> es-discuss mailing list
>>> es-discuss at mozilla.org
>>> https://mail.mozilla.org/listinfo/es-discuss
>


More information about the es-discuss mailing list