Ever wonder why software is so slow...?

Because it's all written by retards.

https://github.com/ArtifexSoftware/jbig2dec/blob/master/jbig2_image.c

Scroll down to jbig2_image_compose_unopt()... and then facepalm. It doesn't take a genius to realise that twiddling an image pixel-by-pixel is going to be dead slow.

>>5
Actually I just finished optimising it with MMX, and got a good ~2x performance improvement overall.

>>6
It's also being used as part of a PDF renderer. I was wondering why large PDFs were taking so long to render, did a little profiling and found that little bastard.