I'm using long double in a C program to compute 2D images of the Mandelbrot Set but wish to have further precision to zoom deeper.
Are there any performance gains to be had from an arbitrary precision maths library that can restrict the amount of precision as required, rather than leaping from long double precision straight into arbitrary precision?
Which is the fastest of the arbitrary precision maths libraries?
'fastest' is going to be somewhat dependent on your platform and intended use.
This wiki article contains links to several libraries.