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- #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;
- }
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