src/libm/s_scalbn.c
changeset 2756 a98604b691c8
child 3162 dc1eb82ffdaa
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/libm/s_scalbn.c	Mon Sep 15 06:33:23 2008 +0000
@@ -0,0 +1,79 @@
+/* @(#)s_scalbn.c 5.1 93/09/24 */
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunPro, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ */
+
+#if defined(LIBM_SCCS) && !defined(lint)
+static char rcsid[] =
+    "$NetBSD: s_scalbn.c,v 1.8 1995/05/10 20:48:08 jtc Exp $";
+#endif
+
+/*
+ * 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 "math.h"
+#include "math_private.h"
+
+libm_hidden_proto(copysign)
+#ifdef __STDC__
+     static const double
+#else
+     static double
+#endif
+       two54 = 1.80143985094819840000e+16,      /* 0x43500000, 0x00000000 */
+         twom54 = 5.55111512312578270212e-17,   /* 0x3C900000, 0x00000000 */
+         huge = 1.0e+300, tiny = 1.0e-300;
+
+libm_hidden_proto(scalbn)
+#ifdef __STDC__
+     double scalbn(double x, int n)
+#else
+     double scalbn(x, n)
+     double x;
+     int n;
+#endif
+{
+    int32_t k, hx, lx;
+    EXTRACT_WORDS(hx, lx, x);
+    k = (hx & 0x7ff00000) >> 20;        /* extract exponent */
+    if (k == 0) {               /* 0 or subnormal x */
+        if ((lx | (hx & 0x7fffffff)) == 0)
+            return x;           /* +-0 */
+        x *= two54;
+        GET_HIGH_WORD(hx, 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 */
+        SET_HIGH_WORD(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 */
+    SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20));
+    return x * twom54;
+}
+
+libm_hidden_def(scalbn)