Do we support any 16 bit-per-channel gifs?

- Bert -

On 09.05.2014, at 06:15, Yoshiki Ohshima <Yoshiki.Ohshima at acm.org> wrote:

> Thank you Eliot!
> 
> The one in my previous email was not a real problem, but I noticed
> that Squeak's PNGReader cannot load certain kind of valid PNG files.
> For example, when colorType=0 (grayscale), bits per channel = 16, and
> has tRNS chunk.  An example of such is 'tbwn0g16.png' on
> http://www.schaik.com/pngsuite/pngsuite_trn_png.html.
> 
> On Tue, May 6, 2014 at 3:02 PM, Eliot Miranda <eliot.miranda at gmail.com> wrote:
>> Thanks Yoshiki,
>> 
>>    I'm committing this now
>> 
>> 
>> On Tue, May 6, 2014 at 2:09 PM, Yoshiki Ohshima <Yoshiki.Ohshima at acm.org>
>> wrote:
>>> 
>>> This can be a nitpick of the year, but there is a bug in
>>> InflateStream>>decompressBlock:with:
>>> 
>>> There is a part that reads (toward the end):
>>> 
>>> ------------------------
>>> collection
>>>        replaceFrom: readLimit+1
>>>        to: readLimit + length + 1
>>>        with: collection
>>>        startingAt: readLimit - distance + 1.
>>> ------------------------
>>> 
>>> but here we want to replace "length" bytes in collection, as opposed
>>> to length + 1 bytes, so it has to say:
>>> 
>>> ------------------------
>>> collection
>>>        replaceFrom: readLimit+1
>>>        to: readLimit + length
>>>        with: collection
>>>        startingAt: readLimit - distance + 1.
>>> ------------------------
>>> 
>>> (So is the non-primitive version in FastInflateStream.)
>>> 
>>> The reason it does not matter is that replaceFrom:to:with:startingAt:
>>> does not care about the source and destination being the same and
>>> overlap between them.  Even when the above bug puts one extra bytes in
>>> collection temporarily, the extra byte will be wiped out in the next
>>> iteration of the loop surrounding it.  However, if you try to port
>>> this to a language that does the "right thing" when there is an
>>> overlap, it manifests as a bug.
>>> 
>>> -- Yoshiki
>>> 
>>> P.S.
>>> It was a "rare" delight to point out a bug in Andreas' code^^; We miss
>>> you.
>>> 
>> 
>> 
>> 
>> --
>> best,
>> Eliot
> 
> 
> 
> -- 
> -- Yoshiki
> 


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