Not knowing too much about processor architecture, I don't understand how fixed point can be much faster, since floating point ops are implemented in hardware.. I presume you used integer operations on your fixed point values, but could you explain a bit why it ends up being much faster than floating point?
It all depends on how precise your fixed point values need to be. If you can squeeze them into 8 bits (I could), you can use SSE 128-bit registers to operate on 16 values at a time. It gets even better with AVX, although that wasn't available to me at the time.
So the speedup is not just from going to fixed point, but from managing to use the vector instructions.
Not knowing too much about processor architecture, I don't understand how fixed point can be much faster, since floating point ops are implemented in hardware.. I presume you used integer operations on your fixed point values, but could you explain a bit why it ends up being much faster than floating point?