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diff --git a/ghc/rts/gmp/mpz/sizeinbase.c b/ghc/rts/gmp/mpz/sizeinbase.c
new file mode 100644
index 0000000..51bd555
--- /dev/null
+++ b/ghc/rts/gmp/mpz/sizeinbase.c
@@ -0,0 +1,60 @@
+/* mpz_sizeinbase(x, base) -- return an approximation to the number of
+   character the integer X would have printed in base BASE.  The
+   approximation is never too small.
+
+Copyright (C) 1991, 1993, 1994, 1995 Free Software Foundation, Inc.
+
+This file is part of the GNU MP Library.
+
+The GNU MP 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 MP 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 MP Library; see the file COPYING.LIB.  If not, write to
+the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+MA 02111-1307, USA. */
+
+#include "gmp.h"
+#include "gmp-impl.h"
+#include "longlong.h"
+
+size_t
+#if __STDC__
+mpz_sizeinbase (mpz_srcptr x, int base)
+#else
+mpz_sizeinbase (x, base)
+     mpz_srcptr x;
+     int base;
+#endif
+{
+  mp_size_t size = ABS (x->_mp_size);
+  int lb_base, cnt;
+  size_t totbits;
+
+  /* Special case for X == 0.  */
+  if (size == 0)
+    return 1;
+
+  /* Calculate the total number of significant bits of X.  */
+  count_leading_zeros (cnt, x->_mp_d[size - 1]);
+  totbits = size * BITS_PER_MP_LIMB - cnt;
+
+  if ((base & (base - 1)) == 0)
+    {
+      /* Special case for powers of 2, giving exact result.  */
+
+      count_leading_zeros (lb_base, base);
+      lb_base = BITS_PER_MP_LIMB - lb_base - 1;
+
+      return (totbits + lb_base - 1) / lb_base;
+    }
+  else
+    return (size_t) (totbits * __mp_bases[base].chars_per_bit_exactly) + 1;
+}