Efficient Bicubic filtering code in GLSL?

Question

I\'m wondering if anyone has complete, working, and efficient code to do bicubic texture filtering in glsl. There is this:

http://www.codeproject.com/Articles/236394/Bi-

Answer 1

I think it is possible that the Catmull version could be done with 4 texture lookups by (a) arranging the input texture like a chessboard with alternate slots saved as positives and as negatives, and (b) an associated modification of textureBicubic. That would rely on the contributions/weights w.x/w.w always being negative, and the contributions w.y/w.z always being positive. I haven't double-checked if this is true, or exactly how the modified textureBicubic would look.

... I have verified that w contributions do satisfy the +ve -ve rules.