ref: ea413b4a62be9993e4b63bf237f0b1d482f4aafa
dir: /sys/src/libc/port/atan2.c/
#include <u.h> #include <libc.h> /* atan2 discovers what quadrant the angle is in and calls atan. */ double atan2(double arg1, double arg2) { if(arg1+arg2 == arg1) { if(arg1 >= 0) return PIO2; return -PIO2; } arg1 = atan(arg1/arg2); if(arg2 < 0) { if(arg1 <= 0) return arg1 + PI; return arg1 - PI; } return arg1; }