68 lines
1.2 KiB
C
68 lines
1.2 KiB
C
/*
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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 <u.h>
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#include <libc.h>
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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 temp, e, x, xsq;
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int flag, sign, i;
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flag = 0;
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sign = 0;
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if(arg < 0){
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arg = -arg;
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sign++;
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}
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arg = 2*arg/PIO2; /* 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) {
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if(temp == 0)
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return NaN();
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temp = 1/temp;
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}
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if(sign)
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temp = -temp;
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return temp;
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}
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