ref: 4757debd0b5935dae94944c35c3cac74b14aa209
dir: /sys/src/libc/port/tan.c/
/* floating point tangent A series is used after range reduction. Coefficients are #4285 from Hart & Cheney. (19.74D) */ #include <u.h> #include <libc.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 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/PIO2; /* overflow? */ x = 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 NaN(); temp = 1/temp; } if(sign) temp = -temp; return temp; }