initial check-in, version 0.5.0

src/math/s_scalbln.c

@@ -0,0 +1,61 @@
+/* @(#)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.
+ * ====================================================
+ */
+
+/*
+ * 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"
+
+static const double
+two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
+twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
+huge   = 1.0e+300,
+tiny   = 1.0e-300;
+
+double
+scalbln (double x, long n)
+{
+        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;
+}
+
+double
+scalbn (double x, int n)
+{
+        return scalbln(x, n);
+}