1 files changed, 59 insertions, 0 deletions
diff --git a/src/math/e_atanh.c b/src/math/e_atanh.c
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+
+/* @(#)e_atanh.c 1.3 95/01/18 */
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunSoft, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice 
+ * is preserved.
+ * ====================================================
+ *
+ */
+
+/* atanh(x)
+ * Method :
+ *    1.Reduced x to positive by atanh(-x) = -atanh(x)
+ *    2.For x>=0.5
+ *                  1              2x                          x
+ *      atanh(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------)
+ *                  2             1 - x                      1 - x
+ *      
+ *      For x<0.5
+ *      atanh(x) = 0.5*log1p(2x+2x*x/(1-x))
+ *
+ * Special cases:
+ *      atanh(x) is NaN if |x| > 1 with signal;
+ *      atanh(NaN) is that NaN with no signal;
+ *      atanh(+-1) is +-INF with signal.
+ *
+ */
+
+#include <math.h>
+#include "math_private.h"
+
+static const double one = 1.0, huge = 1e300;
+static const double zero = 0.0;
+
+double
+atanh(double x)
+{
+        double t;
+        int32_t hx,ix;
+        uint32_t lx;
+        EXTRACT_WORDS(hx,lx,x);
+        ix = hx&0x7fffffff;
+        if ((ix|((lx|(-lx))>>31))>0x3ff00000) /* |x|>1 */
+            return (x-x)/(x-x);
+        if(ix==0x3ff00000) 
+            return x/zero;
+        if(ix<0x3e300000&&(huge+x)>zero) return x;      /* x<2**-28 */
+        SET_HIGH_WORD(x,ix);
+        if(ix<0x3fe00000) {             /* x < 0.5 */
+            t = x+x;
+            t = 0.5*log1p(t+t*x/(one-x));
+        } else 
+            t = 0.5*log1p((x+x)/(one-x));
+        if(hx>=0) return t; else return -t;
+}