[poppler] [RFC] Small string optimization in GooString

[Adam Reichold]

Hello,

Am 01.07.2015 um 23:19 schrieb Albert Astals Cid:
> I welcome the interest in making stuff faster but is GooString really the 
> bottleneck in any of the use cases of poppler?

My aim is definitely not making things faster here, it is reducing
memory usage without sacrificing performance. So staying exactly where
we are but getting small strings down to 32 bytes is basically what I
aim for. (All the benchmarks and graphs are anticipatory obedience as to
show that it does not decrease performance.)

> Sure we can probably make it 1% faster and that's great but usually the "slow" 
> stuff is somewhere else, no?

Of course, my profiler tells me that when using the Qt frontend and the
Splash output device with real PDF files and at realistic resolutions,
almost all of the time is spent in deflate and alpha blending. I do have
an idea how to reduce the time Poppler::Page::renderToImage spents
within Splash::compositeBackground but that seems to be a hornet's nest
w.r.t. toolkit politics. :-\ (I did start to try to improve that method
using intrinsincs but have yet to beat GCC's performance with the
result... :-()

> Or have you found some use case that is heavely dependant on GooString speed?

We certainly throw a lot of small strings around and the changes are
reasonably localized (compared for example with just replacing GooString
with std::string everywhere which seems like the right thing to do), so
I guess having some fun doing it and it seeming to work fine would be
reason enough for me.

> Please do not take this as a "stop doing this", i'm sure you're doing it and 
> you're either learning a lot or having fun, so continue doing it and see where 
> we end up :)

Of course, it might not be reason enough to include the patch. Do you
consider taking just the memory layout fix so that the misleading
comment about the final object size is resolved?

Best regards, Adam.

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