Initial project import

tools/v/vlib/math/tanh.v

@@ -0,0 +1,43 @@
+module math
+
+const tanh_p = [
+	-9.64399179425052238628e-1,
+	-9.92877231001918586564e+1,
+	-1.61468768441708447952e+3,
+]
+const tanh_q = [
+	1.12811678491632931402e+2,
+	2.23548839060100448583e+3,
+	4.84406305325125486048e+3,
+]
+
+// tanh returns the hyperbolic tangent of x.
+//
+// special cases are:
+// tanh(±0) = ±0
+// tanh(±inf) = ±1
+// tanh(nan) = nan
+pub fn tanh(x f64) f64 {
+	maxlog := 8.8029691931113054295988e+01 // log(2**127)
+	mut z := abs(x)
+	if z > 0.5 * maxlog {
+		if x < 0 {
+			return f64(-1)
+		}
+		return 1.0
+	} else if z >= 0.625 {
+		s := exp(2.0 * z)
+		z = 1.0 - 2.0 / (s + 1.0)
+		if x < 0 {
+			z = -z
+		}
+	} else {
+		if x == 0 {
+			return x
+		}
+		s := x * x
+		z = x + x * s * ((tanh_p[0] * s + tanh_p[1]) * s + tanh_p[2]) / (((s + tanh_q[0]) * s +
+			tanh_q[1]) * s + tanh_q[2])
+	}
+	return z
+}