2 asin(arg) and acos(arg) return the arcsin, arccos,
3 respectively of their arguments.
5 Arctan is called after appropriate range reduction.
11 static double pio2 = 1.570796326794896619231e0;
28 temp = sqrt(1 - arg*arg);
30 temp = pio2 - atan(temp/arg);
32 temp = atan(arg/temp);
42 if(arg > 1 || arg < -1) {
46 return pio2 - asin(arg);