summary refs log tree commit diff
path: root/sysdeps/ieee754/ldexp.c
diff options
context:
space:
mode:
Diffstat (limited to 'sysdeps/ieee754/ldexp.c')
-rw-r--r--sysdeps/ieee754/ldexp.c145
1 files changed, 145 insertions, 0 deletions
diff --git a/sysdeps/ieee754/ldexp.c b/sysdeps/ieee754/ldexp.c
new file mode 100644
index 0000000000..7e1c74715b
--- /dev/null
+++ b/sysdeps/ieee754/ldexp.c
@@ -0,0 +1,145 @@
+/* Copyright (C) 1992, 1995 Free Software Foundation, Inc.
+This file is part of the GNU C Library.
+
+The GNU C Library is free software; you can redistribute it and/or
+modify it under the terms of the GNU Library General Public License as
+published by the Free Software Foundation; either version 2 of the
+License, or (at your option) any later version.
+
+The GNU C Library is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+Library General Public License for more details.
+
+You should have received a copy of the GNU Library General Public
+License along with the GNU C Library; see the file COPYING.LIB.  If
+not, write to the Free Software Foundation, Inc., 675 Mass Ave,
+Cambridge, MA 02139, USA.  */
+
+/*
+ * Copyright (c) 1985 Regents of the University of California.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms are permitted provided
+ * that: (1) source distributions retain this entire copyright notice and
+ * comment, and (2) distributions including binaries display the following
+ * acknowledgement:  ``This product includes software developed by the
+ * University of California, Berkeley and its contributors'' in the
+ * documentation or other materials provided with the distribution and in
+ * all advertising materials mentioning features or use of this software.
+ * Neither the name of the University nor the names of its contributors may
+ * be used to endorse or promote products derived from this software without
+ * specific prior written permission.
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+#include <ansidecl.h>
+#include <math.h>
+#include <float.h>
+#include "ieee754.h"
+
+double
+DEFUN(ldexp, (x, exp),
+      double x AND int exp)
+{
+  union ieee754_double u;
+  unsigned int exponent;
+
+  u.d = x;
+#define	x u.d
+
+  exponent = u.ieee.exponent;
+
+  /* The order of the tests is carefully chosen to handle
+     the usual case first, with no branches taken.  */
+
+  if (exponent != 0)
+    {
+      /* X is nonzero and not denormalized.  */
+
+      if (exponent <= DBL_MAX_EXP - DBL_MIN_EXP + 1)
+  	{
+	  /* X is finite.  When EXP < 0, overflow is actually underflow.  */
+
+	  exponent += exp;
+
+	  if (exponent != 0)
+	    {
+	      if (exponent <= DBL_MAX_EXP - DBL_MIN_EXP + 1)
+		{
+		  /* In range.  */
+		  u.ieee.exponent = exponent;
+		  return x;
+		}
+
+	      if (exp >= 0)
+	      overflow:
+		{
+		  CONST int negative = u.ieee.negative;
+		  u.d = HUGE_VAL;
+		  u.ieee.negative = negative;
+		  errno = ERANGE;
+		  return u.d;
+		}
+
+	      if (exponent <= - (unsigned int) (DBL_MANT_DIG + 1))
+		{
+		  /* Underflow.  */
+		  CONST int negative = u.ieee.negative;
+		  u.d = 0.0;
+		  u.ieee.negative = negative;
+		  errno = ERANGE;
+		  return u.d;
+		}
+	    }
+
+	  /* Gradual underflow.  */
+	  u.ieee.exponent = 1;
+	  u.d *= ldexp (1.0, (int) exponent - 1);
+	  if (u.ieee.mantissa0 == 0 && u.ieee.mantissa1 == 0)
+	    /* Underflow.  */
+	    errno = ERANGE;
+	  return u.d;
+  	}
+
+      /* X is +-infinity or NaN.  */
+      if (u.ieee.mantissa0 == 0 && u.ieee.mantissa1 == 0)
+  	{
+	  /* X is +-infinity.  */
+	  if (exp >= 0)
+	    goto overflow;
+	  else
+	    {
+	      /* (infinity * number < 1).  With infinite precision,
+		 (infinity / finite) would be infinity, but otherwise it's
+		 safest to regard (infinity / 2) as indeterminate.  The
+		 infinity might be (2 * finite).  */
+	      CONST int negative = u.ieee.negative;
+	      u.d = NAN;
+	      u.ieee.negative = negative;
+	      errno = EDOM;
+	      return u.d;
+	    }
+	}
+
+      /* X is NaN.  */
+      errno = EDOM;
+      return u.d;
+    }
+
+  /* X is zero or denormalized.  */
+  if (u.ieee.mantissa0 == 0 && u.ieee.mantissa1 == 0)
+    /* X is +-0.0. */
+    return x;
+
+  /* X is denormalized.
+     Multiplying by 2 ** DBL_MANT_DIG normalizes it;
+     we then subtract the DBL_MANT_DIG we added to the exponent.  */
+  return ldexp (x * ldexp (1.0, DBL_MANT_DIG), exp - DBL_MANT_DIG);
+}
+
+/* Compatibility names for the same function.  */
+weak_alias (ldexp, __scalb)
+weak_alias (ldexp, scalb)