1 files changed, 53 insertions, 0 deletions
diff --git a/lib/libm/ctan.c b/lib/libm/ctan.c
new file mode 100644
index 00000000..2bc6156c
--- /dev/null
+++ b/lib/libm/ctan.c
@@ -0,0 +1,53 @@
+#include "__complex.h"
+
+double _ctans(double complex z)
+{
+	double f, x, x2, y, y2, rn, t;
+	double d;
+	x = fabs(2.0 * creal(z));
+	y = fabs(2.0 * cimag(z));
+	x = redupi(x);
+	x = x * x;
+	y = y * y;
+	x2 = 1.0;
+	y2 = 1.0;
+	f = 1.0;
+	rn = 0.0;
+	d = 0.0;
+	do {
+		rn += 1.0;
+		f *= rn;
+		rn += 1.0;
+		f *= rn;
+		x2 *= x;
+		y2 *= y;
+		t = y2 + x2;
+		t /= f;
+		d += t;
+		rn += 1.0;
+		f *= rn;
+		rn += 1.0;
+		f *= rn;
+		x2 *= x;
+		y2 *= y;
+		t = y2 - x2;
+		t /= f;
+		d += t;
+	} while (fabs(t / d) > MACHEP);
+	return d;
+}
+
+double complex ctan(double complex z)
+{
+	double d = cos(2.0 * creal(z)) + cosh(2.0 * cimag(z));
+
+	if (fabs(d) < 0.25)
+		d = _ctans(z);
+
+	if (d == 0.0) {
+		return HUGE_VAL + HUGE_VAL * (double complex)I;
+	}
+
+	return sin(2.0 * creal(z)) / d +
+	       (sinh(2.0 * cimag(z)) / d) * (double complex)I;
+}