20060303a

1 files changed, 55 insertions, 0 deletions

diff --git a/libmath/fdlibm/s_scalbn.c b/libmath/fdlibm/s_scalbn.c
new file mode 100644
index 00000000..cb80aecb
--- /dev/null
+++ b/libmath/fdlibm/s_scalbn.c
@@ -0,0 +1,55 @@
+/* derived from /netlib/fdlibm */
+
+/* @(#)s_scalbn.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.
+ * ====================================================
+ */
+
+/* 
+ * scalbn (double x, int n)
+ * scalbn(x,n) returns x* 2**n  computed by  exponent  
+ * manipulation rather than by actually performing an 
+ * exponentiation or a multiplication.
+ */
+
+#include "fdlibm.h"
+
+static const double
+two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
+twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
+Huge   = 1.0e+300,
+tiny   = 1.0e-300;
+
+	double scalbn (double x, int n)
+{
+	int  k,hx,lx;
+	hx = __HI(x);
+	lx = __LO(x);
+        k = (hx&0x7ff00000)>>20;		/* extract exponent */
+        if (k==0) {				/* 0 or subnormal x */
+            if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
+	    x *= two54; 
+	    hx = __HI(x);
+	    k = ((hx&0x7ff00000)>>20) - 54; 
+            if (n< -50000) return tiny*x; 	/*underflow*/
+	    }
+        if (k==0x7ff) return x+x;		/* NaN or Inf */
+        k = k+n; 
+        if (k >  0x7fe) return Huge*copysign(Huge,x); /* overflow  */
+        if (k > 0) 				/* normal result */
+	    {__HI(x) = (hx&0x800fffff)|(k<<20); return x;}
+        if (k <= -54)
+            if (n > 50000) 	/* in case integer overflow in n+k */
+		return Huge*copysign(Huge,x);	/*overflow*/
+	    else return tiny*copysign(tiny,x); 	/*underflow*/
+        k += 54;				/* subnormal result */
+        __HI(x) = (hx&0x800fffff)|(k<<20);
+        return x*twom54;
+}