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diff --git a/src/math/s_tanh.c b/src/math/s_tanh.c
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+/* @(#)s_tanh.c 5.1 93/09/24 */
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunPro, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ */
+
+/* Tanh(x)
+ * Return the Hyperbolic Tangent of x
+ *
+ * Method :
+ *                                     x    -x
+ *                                    e  - e
+ *      0. tanh(x) is defined to be -----------
+ *                                     x    -x
+ *                                    e  + e
+ *      1. reduce x to non-negative by tanh(-x) = -tanh(x).
+ *      2.  0      <= x <= 2**-55 : tanh(x) := x*(one+x)
+ *                                              -t
+ *          2**-55 <  x <=  1     : tanh(x) := -----; t = expm1(-2x)
+ *                                             t + 2
+ *                                                   2
+ *          1      <= x <=  22.0  : tanh(x) := 1-  ----- ; t=expm1(2x)
+ *                                                 t + 2
+ *          22.0   <  x <= INF    : tanh(x) := 1.
+ *
+ * Special cases:
+ *      tanh(NaN) is NaN;
+ *      only tanh(0)=0 is exact for finite argument.
+ */
+
+#include <math.h>
+#include "math_private.h"
+
+static const double one=1.0, two=2.0, tiny = 1.0e-300;
+
+double
+tanh(double x)
+{
+        double t,z;
+        int32_t jx,ix;
+
+    /* High word of |x|. */
+        GET_HIGH_WORD(jx,x);
+        ix = jx&0x7fffffff;
+
+    /* x is INF or NaN */
+        if(ix>=0x7ff00000) {
+            if (jx>=0) return one/x+one;    /* tanh(+-inf)=+-1 */
+            else       return one/x-one;    /* tanh(NaN) = NaN */
+        }
+
+    /* |x| < 22 */
+        if (ix < 0x40360000) {          /* |x|<22 */
+            if (ix<0x3c800000)          /* |x|<2**-55 */
+                return x*(one+x);       /* tanh(small) = small */
+            if (ix>=0x3ff00000) {       /* |x|>=1  */
+                t = expm1(two*fabs(x));
+                z = one - two/(t+two);
+            } else {
+                t = expm1(-two*fabs(x));
+                z= -t/(t+two);
+            }
+    /* |x| > 22, return +-1 */
+        } else {
+            z = one - tiny;             /* raised inexact flag */
+        }
+        return (jx>=0)? z: -z;
+}