Speed optimizations

[GoogleCodeExporter]

APV is usually fast, and sometimes slow on some PDF files.
It may be related to jpeg decompression.
Maybe some options in libjpeg can be activated to speed up APV (or add an arm 
optimized idct)

Original issue reported on code.google.com by ldro...@gmail.com on 23 Nov 2010 at 10:13

[GoogleCodeExporter]

One speed optimization I just committed was to add -O3 to the lib compile flags 
and compile to arm rather than thumb.  

Can you attach a file where the problem occurs?

Original comment by arpruss on 25 Jul 2011 at 5:37

[GoogleCodeExporter]

All pdf files containing JPEG images are slow to render.
I started to work on this a few months ago, and found that the jpeg idct may 
not be optimized for arm...

Original comment by ldro...@gmail.com on 27 Jul 2011 at 2:43

[GoogleCodeExporter]

I switched jpeglib to the fast (but less accurate) idct.  I didn't benchmark, 
but it feels slightly faster.  I tried the floating point, but it seemed slower.

Original comment by arpruss on 31 Jul 2011 at 2:50

[GoogleCodeExporter]

Here is a NEON-optimized libjpeg: http://sourceforge.net/projects/libjpeg-turbo/

We'd need to add detection for NEON, and this would only go in the armv7-a 
version of the library.

Original comment by arpruss on 31 Jul 2011 at 3:15

[GoogleCodeExporter]

There was a problem in the threading model which caused the same tiles to get 
rendered multiple times.  The problem was that the cache was checked when the 
tiles were fed to a worker thread rather than just before rendering.  I fixed 
this.

Original comment by arpruss on 31 Jul 2011 at 3:22

[GoogleCodeExporter]

I think that by default, the fast idct is used. But maybe on some CPUs, the fp 
idct is faster ? (good to hear that you found a bug in the cache, I was 
suspecting this but I didn't spot it !)

Original comment by ldro...@gmail.com on 2 Aug 2011 at 12:26

[GoogleCodeExporter]

I think you're right: the fast one was used.  I switched to float on CPUs that 
have an FPU--I don't know if that improved performance, but at least it should 
improve quality.

Original comment by arpruss on 3 Aug 2011 at 2:48