1 files changed, 92 insertions, 0 deletions
diff --git a/libm/float/atanhf.c b/libm/float/atanhf.c
new file mode 100644
index 000000000..dfadad09e
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+++ b/libm/float/atanhf.c
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+/*							atanhf.c
+ *
+ *	Inverse hyperbolic tangent
+ *
+ *
+ *
+ * SYNOPSIS:
+ *
+ * float x, y, atanhf();
+ *
+ * y = atanhf( x );
+ *
+ *
+ *
+ * DESCRIPTION:
+ *
+ * Returns inverse hyperbolic tangent of argument in the range
+ * MINLOGF to MAXLOGF.
+ *
+ * If |x| < 0.5, a polynomial approximation is used.
+ * Otherwise,
+ *        atanh(x) = 0.5 * log( (1+x)/(1-x) ).
+ *
+ *
+ *
+ * ACCURACY:
+ *
+ *                      Relative error:
+ * arithmetic   domain     # trials      peak         rms
+ *    IEEE      -1,1        100000      1.4e-7      3.1e-8
+ *
+ */
+
+/*						atanh.c	*/
+
+
+/*
+Cephes Math Library Release 2.2:  June, 1992
+Copyright (C) 1987, 1992 by Stephen L. Moshier
+Direct inquiries to 30 Frost Street, Cambridge, MA 02140
+*/
+
+/* Single precision inverse hyperbolic tangent
+ * test interval: [-0.5, +0.5]
+ * trials: 10000
+ * peak relative error: 8.2e-8
+ * rms relative error: 3.0e-8
+ */
+#include <math.h>
+extern float MAXNUMF;
+
+float logf( float );
+
+float atanhf( float xx )
+{
+float x, z;
+
+x = xx;
+if( x < 0 )
+	z = -x;
+else
+	z = x;
+if( z >= 1.0 )
+	{
+	if( x == 1.0 )
+		return( MAXNUMF );
+	if( x == -1.0 )
+		return( -MAXNUMF );
+	mtherr( "atanhl", DOMAIN );
+	return( MAXNUMF );
+	}
+
+if( z < 1.0e-4 )
+	return(x);
+
+if( z < 0.5 )
+	{
+	z = x * x;
+	z =
+	(((( 1.81740078349E-1 * z
+	  + 8.24370301058E-2) * z
+	  + 1.46691431730E-1) * z
+	  + 1.99782164500E-1) * z
+	  + 3.33337300303E-1) * z * x
+	  + x;
+	}
+else
+	{
+	z = 0.5 * logf( (1.0+x)/(1.0-x) );
+	}
+return( z );
+}