1. There is no C function.<p>2. Inlining in an actual C implementation doesn't matter because there is no register pressure and each trig function generates a real function call.  Function calls to known addresses are really fast (~2 cycles), even indirect calls are fast compared to transcendental functions (~ 6 cycles).  For comparison, the C implementation takes ~260 cycles each distance computation.  This can't be improved much without vectorizing the trig functions.