add fdlibm

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

external/fdlibm/e_acosh.c

@@ -0,0 +1,55 @@
+
+/* @(#)e_acosh.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_acosh(x)
+ * Method :
+ *	Based on
+ *		acosh(x) = log [ x + sqrt(x*x-1) ]
+ *	we have
+ *		acosh(x) := log(x)+ln2,	if x is large; else
+ *		acosh(x) := log(2x-1/(sqrt(x*x-1)+x)) if x>2; else
+ *		acosh(x) := log1p(t+sqrt(2.0*t+t*t)); where t=x-1.
+ *
+ * Special cases:
+ *	acosh(x) is NaN with signal if x<1.
+ *	acosh(NaN) is NaN without signal.
+ */
+
+#include "math.h"
+
+static const double
+    one = 1.0,
+    ln2 = 6.93147180559945286227e-01; /* 0x3FE62E42, 0xFEFA39EF */
+
+double __fdlibm_acosh(double x) {
+	double t;
+	int    hx;
+	hx = __HI(x);
+	if(hx < 0x3ff00000) { /* x < 1 */
+		return (x - x) / (x - x);
+	} else if(hx >= 0x41b00000) {  /* x > 2**28 */
+		if(hx >= 0x7ff00000) { /* x is inf of NaN */
+			return x + x;
+		} else
+			return __fdlibm_log(x) + ln2; /* acosh(hugev)=log(2x) */
+	} else if(((hx - 0x3ff00000) | __LO(x)) == 0) {
+		return 0.0;	     /* acosh(1) = 0 */
+	} else if(hx > 0x40000000) { /* 2**28 > x > 2 */
+		t = x * x;
+		return __fdlibm_log(2.0 * x - one / (x + sqrt(t - one)));
+	} else { /* 1<x<2 */
+		t = x - one;
+		return log1p(t + sqrt(2.0 * t + t * t));
+	}
+}