Benchmark: timing 1 iterations of uv_fits_double3, uv_fits_double_bitfiddle...
uv_fits_double3:  1 wallclock secs ( 0.45 usr +  0.00 sys =  0.45 CPU) @  2.21/s (n=1)
            (warning: too few iterations for a reliable count)
uv_fits_double_bitfiddle:  0 wallclock secs ( 0.25 usr +  0.00 sys =  0.25 CPU)@  4.02/s (n=1)
            (warning: too few iterations for a reliable count)