post processing, color grading in shaders

I'm using Unity's built-in render pipeline in a research application. The color grading effect in the post-processing stack could be a really useful tool for me, but I need to know exactly how it adjusts color. I understand it in broad outline, but I need to know the specific calculations that it does. So my question is: can someone point me to the code that implements color grading in the BRP? I'm particularly interested in how the Lookup Texture (LUT) feature works.

I spent some time looking at the Graphics github repo before realizing that that code is for the SRP. Other than that, it was exactly what I was looking for. Is corresponding code available for reference for the BRP?

Thanks!