1 files changed, 42 insertions, 0 deletions
diff --git a/src/int_ceil_log2.c b/src/int_ceil_log2.c
new file mode 100644
index 000000000..de6052e36
--- /dev/null
+++ b/src/int_ceil_log2.c
@@ -0,0 +1,42 @@
+/* __gmpfr_int_ceil_log2 -- Integer ceil of log2(x)
+
+Copyright 2004, 2005, 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
+Contributed by the Arenaire 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. */
+
+#define MPFR_NEED_LONGLONG_H /* for count_leading_zeros */
+#include "mpfr-impl.h"
+
+int
+__gmpfr_int_ceil_log2 (unsigned long n)
+{
+  if (MPFR_UNLIKELY (n == 1))
+    return 0;
+  else
+    {
+      int b;
+      mp_limb_t limb;
+
+      MPFR_ASSERTN (n > 1);
+      limb = n - 1;
+      MPFR_ASSERTN (limb == n - 1);
+      count_leading_zeros (b, limb);
+      return GMP_NUMB_BITS - b;
+    }
+}