Re: [Lcms-user] Threading performance in LCMS2

[Richard H. <hug...@gm...>]

On 14 May 2013 00:32, Robin Watts <rob...@ar...> wrote:
> Before you dive into the complexities of multithreading etc, it would
> seem sensible to ensure you are getting the best possible performance
> out of the transform routine in the first place.

Makes sense.

> LCMS has various different transform routines built in; by using a
> cunning scheme, it can pick the appropriate one at runtime. If there
> happens to be one in its repertoire that exactly fits your needs, it can
> run considerably faster than if it has to use a generic one.

Other than profiling, how do we know if it's chosen a built-in version
rather than the generic version?

> To speed ghostscripts use of lcms2, I wanted to optimise the transforms
> that we use as much as possible. But we use quite a lot of them, and I
> didn't want to have to hand write optimised ones for all of the
> different cases. So I implemented a system that uses a chameleonic
> header; set a few options with #defines, and include the header, and it
> makes the optimised transform function for you.

I see, https://github.com/robinwatts/Little-CMS/blob/artifex/src/cmsxform.h
-- that looks pretty magic, is there no way to do that without the
#preprocessor trickery?

> He did however point out that I could recast the code slightly as a
> plugin for lcms 2. This gives the same benefits without polluting the
> internals of the library itself. I plan to do this at some point, but I
> have not got round to it yet.

Yes, that would be awesome.

Thanks,

Richard.