add fdlibm

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

external/fdlibm/e_cosh.c

@@ -0,0 +1,79 @@
+
+/* @(#)e_cosh.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_cosh(x)
+ * Method :
+ * mathematically cosh(x) if defined to be (exp(x)+exp(-x))/2
+ *	1. Replace x by |x| (cosh(x) = cosh(-x)).
+ *	2.
+ *		                                        [ exp(x) - 1 ]^2
+ *	    0        <= x <= ln2/2  :  cosh(x) := 1 + -------------------
+ *			       			           2*exp(x)
+ *
+ *		                                  exp(x) +  1/exp(x)
+ *	    ln2/2    <= x <= 22     :  cosh(x) := -------------------
+ *			       			          2
+ *	    22       <= x <= lnovft :  cosh(x) := exp(x)/2
+ *	    lnovft   <= x <= ln2ovft:  cosh(x) := exp(x/2)/2 * exp(x/2)
+ *	    ln2ovft  <  x	    :  cosh(x) := hugev*hugev (overflow)
+ *
+ * Special cases:
+ *	cosh(x) is |x| if x is +INF, -INF, or NaN.
+ *	only cosh(0)=1 is exact for finite x.
+ */
+
+#include "math.h"
+
+static const double one = 1.0, half = 0.5, hugev = 1.0e300;
+
+double __fdlibm_cosh(double x) {
+	double	 t, w;
+	int	 ix;
+	unsigned lx;
+
+	/* High word of |x|. */
+	ix = __HI(x);
+	ix &= 0x7fffffff;
+
+	/* x is INF or NaN */
+	if(ix >= 0x7ff00000) return x * x;
+
+	/* |x| in [0,0.5*ln2], return 1+expm1(|x|)^2/(2*exp(|x|)) */
+	if(ix < 0x3fd62e43) {
+		t = expm1(fabs(x));
+		w = one + t;
+		if(ix < 0x3c800000) return w; /* cosh(tinyv) = 1 */
+		return one + (t * t) / (w + w);
+	}
+
+	/* |x| in [0.5*ln2,22], return (exp(|x|)+1/exp(|x|)/2; */
+	if(ix < 0x40360000) {
+		t = __fdlibm_exp(fabs(x));
+		return half * t + half / t;
+	}
+
+	/* |x| in [22, log(maxdouble)] return half*exp(|x|) */
+	if(ix < 0x40862E42) return half * __fdlibm_exp(fabs(x));
+
+	/* |x| in [log(maxdouble), overflowthresold] */
+	lx = *((((*(unsigned*)&one) >> 29)) + (unsigned*)&x);
+	if(ix < 0x408633CE ||
+	   (ix == 0x408633ce) && (lx <= (unsigned)0x8fb9f87d)) {
+		w = __fdlibm_exp(half * fabs(x));
+		t = half * w;
+		return t * w;
+	}
+
+	/* |x| > overflowthresold, cosh(x) overflow */
+	return hugev * hugev;
+}