I'm writing a fairly extensive pixel shader, using D3D11 and targetting shader model 4. As it stands I currently mix float's and int's a fair amount. I'm under the assumption, but haven't been able to find any definitive information, that casting between int and float in a pixel shader would incur some performance overhead. I could simplify a lot of the code and change it all to float's, but in a few places I need to do a fast 2^x multiply or divide, which with int's can be performed with a bit-shift.

Is there anyway to do a fast 2^x multiply with floats? Or, I was under the impression that with older hlsl targets that ints were just emulated with the mantissa portion of the float and perhaps that's still the case and casting between and float and int is simply a signal to the compiler and actually doesn't require an op?

I'd like to write both versions and give it a try, but its fairly extensive and at the moment I don't have the time. Given the circumstances what would you choose?

exp2
http://msdn.microsoft.com/en-us/library/windows/desktop/bb509596%28v=vs.85%29.aspx

The only way to find out the answer to your question is to test performance. You can also get an idea by looking at the token assembly of your shader.

Also, integers operations were emulated with floats in DirectX 9, but 10 requires full integer support. I don't see how they could simulate it with a float, and if they did you would notice a huge performance impact.