add fdlibm

git-svn-id: http://svn2.nishi.boats/svn/milsko/trunk@557 b9cfdab3-6d41-4d17-bbe4-086880011989

external/fdlibm/e_atanh.c

@@ -0,0 +1,60 @@
+
+/* @(#)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.
+ * ====================================================
+ *
+ */
+
+/* __fdlibm_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"
+
+static const double one = 1.0, hugev = 1e300;
+
+static double zero = 0.0;
+
+double __fdlibm_atanh(double x) {
+	double	 t;
+	int	 hx, ix;
+	unsigned lx;
+	hx = __HI(x); /* high word */
+	lx = __LO(x); /* low word */
+	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 && (hugev + x) > zero) return x; /* x<2**-28 */
+	__HI(x) = ix;					    /* x <- |x| */
+	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;
+}