1 files changed, 52 insertions, 0 deletions
diff --git a/test/math/etanh.c b/test/math/etanh.c
new file mode 100644
index 000000000..c74b4700a
--- /dev/null
+++ b/test/math/etanh.c
@@ -0,0 +1,52 @@
+/*							xtanh.c		*/
+/* hyperbolic tangent check routine */
+/* this subroutine is used by the exponential function routine */
+/* by Stephen L. Moshier. */
+
+
+
+#include "ehead.h"
+
+
+void etanh( x, y )
+unsigned short *x, *y;
+{
+unsigned short e[NE], r[NE], j[NE], xx[NE], m2[NE];
+short i, n;
+long lj;
+
+emov( x, r );
+r[NE-1] &= (unsigned short )0x7fff;
+if( ecmp(r, eone) >= 0 )
+	{
+/* tanh(x) = (exp(x) - exp(-x)) / (exp(x) + exp(-x))
+ * Note eexp() calls xtanh, but with an argument less than (1 + log 2)/2.
+ */
+	eexp( r, e );
+	ediv( e, eone, r );
+	esub( r, e, xx );
+	eadd( r, e, j );
+	ediv( j, xx, y );
+	return;
+	}
+
+emov( etwo, m2 );
+eneg( m2 );
+
+n = NBITS/8;	/* Number of terms to do in the continued fraction */
+lj = 2 * n + 1;
+ltoe( &lj, j );
+
+emov( j, e );
+emul( x, x, xx );
+
+/* continued fraction */
+for( i=0; i<n; i++)
+	{
+	ediv( e, xx, r );
+	eadd( m2, j, j );
+	eadd( r, j, e );
+	}
+
+ediv( e, x, y );
+}