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WebSVN – planix.SVN – Blame – /os/branches/feature_fixcpp/sys/src/ape/lib/ap/math/tan.c – Rev 2

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/*
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	floating point tangent
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	A series is used after range reduction.
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	Coefficients are #4285 from Hart & Cheney. (19.74D)
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 */
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#include <math.h>
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#include <errno.h>
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static double invpi	  = 1.27323954473516268;
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static double p0	 = -0.1306820264754825668269611177e+5;
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static double p1	  = 0.1055970901714953193602353981e+4;
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static double p2	 = -0.1550685653483266376941705728e+2;
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static double p3	  = 0.3422554387241003435328470489e-1;
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static double p4	  = 0.3386638642677172096076369e-4;
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static double q0	 = -0.1663895238947119001851464661e+5;
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static double q1	  = 0.4765751362916483698926655581e+4;
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static double q2	 = -0.1555033164031709966900124574e+3;
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double
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tan(double arg)
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{
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	double sign, temp, e, x, xsq;
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	int flag, i;
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	flag = 0;
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	sign = 1;
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	if(arg < 0){
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		arg = -arg;
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		sign = -1;
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	}
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	arg = arg*invpi;   /* overflow? */
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	x = modf(arg, &e);
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	i = e;
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	switch(i%4) {
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	case 1:
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		x = 1 - x;
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		flag = 1;
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		break;
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	case 2:
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		sign = - sign;
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		flag = 1;
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		break;
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	case 3:
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		x = 1 - x;
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		sign = - sign;
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		break;
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	case 0:
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		break;
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	}
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	xsq = x*x;
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	temp = ((((p4*xsq+p3)*xsq+p2)*xsq+p1)*xsq+p0)*x;
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	temp = temp/(((xsq+q2)*xsq+q1)*xsq+q0);
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	if(flag == 1) {
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		if(temp == 0) {
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			errno = EDOM;
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			if (sign > 0)
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				return HUGE_VAL;
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			return -HUGE_VAL;
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		}
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		temp = 1/temp;
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	}
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	return sign*temp;
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}