1 files changed, 91 insertions, 0 deletions
diff --git a/src/scale2.c b/src/scale2.c
new file mode 100644
index 0000000..5de38c3
--- /dev/null
+++ b/src/scale2.c
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+/* mpfr_scale2 -- multiply a double float by 2^exp
+
+Copyright 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Free Software Foundation, Inc.
+Contributed by the AriC and Caramel projects, INRIA.
+
+This file is part of the GNU MPFR Library.
+
+The GNU MPFR Library is free software; you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation; either version 3 of the License, or (at your
+option) any later version.
+
+The GNU MPFR 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 Lesser General Public
+License for more details.
+
+You should have received a copy of the GNU Lesser General Public License
+along with the GNU MPFR Library; see the file COPYING.LESSER.  If not, see
+http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
+51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
+
+#include <float.h> /* for DBL_EPSILON */
+#include "mpfr-impl.h"
+
+/* Note: we could use the ldexp function, but since we want not to depend on
+   math.h, we write our own implementation. */
+
+/* multiplies 1/2 <= d <= 1 by 2^exp */
+double
+mpfr_scale2 (double d, int exp)
+{
+#if _GMP_IEEE_FLOATS
+  {
+    union ieee_double_extract x;
+
+    if (MPFR_UNLIKELY (d == 1.0))
+      {
+        d = 0.5;
+        exp ++;
+      }
+
+    /* now 1/2 <= d < 1 */
+
+    /* infinities and zeroes have already been checked */
+    MPFR_ASSERTD (-1073 <= exp && exp <= 1025);
+
+    x.d = d;
+    if (MPFR_UNLIKELY (exp < -1021)) /* subnormal case */
+      {
+        x.s.exp += exp + 52;
+        x.d *= DBL_EPSILON;
+      }
+    else /* normalized case */
+      {
+        x.s.exp += exp;
+      }
+    return x.d;
+  }
+#else /* _GMP_IEEE_FLOATS */
+  {
+    double factor;
+
+    /* An overflow may occurs (example: 0.5*2^1024) */
+    if (d < 1.0)
+      {
+        d += d;
+        exp--;
+      }
+    /* Now 1.0 <= d < 2.0 */
+
+    if (exp < 0)
+      {
+        factor = 0.5;
+        exp = -exp;
+      }
+    else
+      {
+        factor = 2.0;
+      }
+    while (exp != 0)
+      {
+        if ((exp & 1) != 0)
+          d *= factor;
+        exp >>= 1;
+        factor *= factor;
+      }
+    return d;
+  }
+#endif
+}