1 files changed, 67 insertions, 0 deletions
diff --git a/src/base/math/tan.c b/src/base/math/tan.c
new file mode 100644
index 0000000..08b8806
--- /dev/null
+++ b/src/base/math/tan.c
@@ -0,0 +1,67 @@
+/*
+	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;
+}