20060303a

1 files changed, 57 insertions, 0 deletions

diff --git a/libmath/fdlibm/e_acosh.c b/libmath/fdlibm/e_acosh.c
new file mode 100644
index 00000000..48fd4faa
--- /dev/null
+++ b/libmath/fdlibm/e_acosh.c
@@ -0,0 +1,57 @@
+/* derived from /netlib/fdlibm */
+
+/* @(#)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.
+ * ====================================================
+ *
+ */
+
+/* __ieee754_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 "fdlibm.h"
+
+static const double 
+one	= 1.0,
+ln2	= 6.93147180559945286227e-01;  /* 0x3FE62E42, 0xFEFA39EF */
+
+	double __ieee754_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 __ieee754_log(x)+ln2;	/* acosh(Huge)=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 __ieee754_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));
+	}
+}