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/*
floating point tangent
A series is used after range reduction.
Coefficients are #4285 from Hart & Cheney. (19.74D)
*/
#include <u.h>
#include <base.h>
static double p0 = -0.1306820264754825668269611177e+5;
static double p1 = 0.1055970901714953193602353981e+4;
static double p2 = -0.1550685653483266376941705728e+2;
static double p3 = 0.3422554387241003435328470489e-1;
static double p4 = 0.3386638642677172096076369e-4;
static double q0 = -0.1663895238947119001851464661e+5;
static double q1 = 0.4765751362916483698926655581e+4;
static double q2 = -0.1555033164031709966900124574e+3;
double
math·tan(double arg)
{
double temp, e, x, xsq;
int flag, sign, i;
flag = 0;
sign = 0;
if(arg < 0){
arg = -arg;
sign++;
}
arg = 2*arg/math·PIO2; /* overflow? */
x = math·modf(arg, &e);
i = e;
switch(i%4) {
case 1:
x = 1 - x;
flag = 1;
break;
case 2:
sign = !sign;
flag = 1;
break;
case 3:
x = 1 - x;
sign = !sign;
break;
case 0:
break;
}
xsq = x*x;
temp = ((((p4*xsq+p3)*xsq+p2)*xsq+p1)*xsq+p0)*x;
temp = temp/(((xsq+q2)*xsq+q1)*xsq+q0);
if(flag) {
if(temp == 0)
return math·NaN();
temp = 1/temp;
}
if(sign)
temp = -temp;
return temp;
}
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