Does the GLSL sign() function cause branching and how does it work?

Question

It seems like some functions that have outputs in cases might use an if statement as the underlying implementation, thus causing branching. I don't think it does, but I wonder.

For sign(x), if the number is positive, negative, or zero, it reruns 1, -1 and 0 respectively.

So how does this function work?

Answer 1

Implementation details are always implementation-specific. So how this construct is implemented depends entirely on the vendor (and ultimatively, the abilities of the underlying hardware).

However, it is extremely unlikely that any real-world implementation would use a branch for the sign() opertation. The sign can be easily determined by looking at the sign bit which is present in most real-world floating-point formats, especially IEE 754. This can be easily implemented with logic - much easier as your typical floating point arithmetic function.