1 files changed, 88 insertions, 0 deletions
diff --git a/libm/float/tanhf.c b/libm/float/tanhf.c
new file mode 100644
index 000000000..4636192c2
--- /dev/null
+++ b/libm/float/tanhf.c
@@ -0,0 +1,88 @@
+/*							tanhf.c
+ *
+ *	Hyperbolic tangent
+ *
+ *
+ *
+ * SYNOPSIS:
+ *
+ * float x, y, tanhf();
+ *
+ * y = tanhf( x );
+ *
+ *
+ *
+ * DESCRIPTION:
+ *
+ * Returns hyperbolic tangent of argument in the range MINLOG to
+ * MAXLOG.
+ *
+ * A polynomial approximation is used for |x| < 0.625.
+ * Otherwise,
+ *
+ *    tanh(x) = sinh(x)/cosh(x) = 1  -  2/(exp(2x) + 1).
+ *
+ *
+ *
+ * ACCURACY:
+ *
+ *                      Relative error:
+ * arithmetic   domain     # trials      peak         rms
+ *    IEEE      -2,2        100000      1.3e-7      2.6e-8
+ *
+ */
+
+/*
+Cephes Math Library Release 2.2:  June, 1992
+Copyright 1984, 1987, 1989, 1992 by Stephen L. Moshier
+Direct inquiries to 30 Frost Street, Cambridge, MA 02140
+*/
+
+/* Single precision hyperbolic tangent
+ * test interval: [-0.625, +0.625]
+ * trials: 10000
+ * peak relative error: 7.2e-8
+ * rms relative error: 2.6e-8
+ */
+#include <math.h>
+
+extern float MAXLOGF;
+
+float expf( float );
+
+float tanhf( float xx )
+{
+float x, z;
+
+if( xx < 0 )
+	x = -xx;
+else
+	x = xx;
+
+if( x > 0.5 * MAXLOGF )
+	{
+	if( xx > 0 )
+		return( 1.0 );
+	else
+		return( -1.0 );
+	}
+if( x >= 0.625 )
+	{
+	x = expf(x+x);
+	z =  1.0  - 2.0/(x + 1.0);
+	if( xx < 0 )
+		z = -z;
+	}
+else
+	{
+	z = x * x;
+	z =
+	(((( -5.70498872745E-3 * z
+	  + 2.06390887954E-2) * z
+	  - 5.37397155531E-2) * z
+	  + 1.33314422036E-1) * z
+	  - 3.33332819422E-1) * z * xx
+	  + xx;
+	}
+return( z );
+}