- CPUs can do 64x64 multiplies that give 128-bit results. GPUs cannot.
- CPUs can do add-with-carry. GPUs cannot.<p>That means that GPUs are not very good at doing high-precision math. They lose a lot more efficiency implementing high-precision math than CPUs do. And GPUs are also worse at doing parallel calculations that end up following different paths, which inevitably happens when one pixel diverges before another.<p>My back-of-the-envelope estimates show that GPUs are not worth it for this use-case. I will change my mind when I see a GPU-based deep zoom fractal program.