tjCompress2 does not perform high compression

[espresso3389]

I've been evaluating MozJpeg's tjCompress2 function using tjexample (with only input/output filenames but no more options).
The problem is that the latest master commit (1a7384c) does "normal" JPEG compression and the result seems to be identical to normal libjpeg-turbo.

• It seem the last commit that works well is 6d95c51.
• bit bisect start HEAD 6d95c51a indicates that the ultimate cause is 044c22e, that is on libjpeg-turbo 2.0.5 branch.
• And the commit b3e7390 (that merges the branch) broke the master branch.

I've checked the commit, 044c22e, but I could not found anything related to the actual behavior but there're changes on unit tests... :(

[kornelski]

I didn't think anyone used this API instead of the standard libjpeg API.

MozJPEG reuses unit tests from libjpeg-trubo, and it happens that unit tests rely on this function being bit-identical to libjpeg-turbo.

[espresso3389]

If so, please document the fact somewhere.

FYI, at least, MozJpegSharp depends on the function.

[kornelski]

Ok. I'll try to make it work with improved compression.

[PJK136]

I think it's the same problem I have with #381.

I just dirtily reverted f1d512d to make it works, but I'm interested in a proper fix/workaround too.