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#include <math.h>
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#include <errno.h>
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/*
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	atan2 discovers what quadrant the angle
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	is in and calls atan.
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*/
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#define pio2 1.5707963267948966192313217
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#define pi   3.1415926535897932384626434;
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double
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atan2(double arg1, double arg2)
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{
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	if(arg1 == 0.0 && arg2 == 0.0){
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		errno = EDOM;
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		return 0.0;
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	}
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	if(arg1+arg2 == arg1) {
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		if(arg1 >= 0)
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			return pio2;
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		return -pio2;
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	}
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	arg1 = atan(arg1/arg2);
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	if(arg2 < 0) {
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		if(arg1 <= 0)
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			return arg1 + pi;
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		return arg1 - pi;
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	}
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	return arg1;
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}