1 files changed, 59 insertions, 0 deletions
diff --git a/src/math/atanh.c b/src/math/atanh.c
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+++ b/src/math/atanh.c
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+/* origin: FreeBSD /usr/src/lib/msun/src/e_atanh.c */
+/*
+ * ====================================================
+ * 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 "libm.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)  /* x < 2**-28 */
+		return x;
+	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;
+	return -t;
+}