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diff --git a/gmp/mpz/clrbit.c b/gmp/mpz/clrbit.c
new file mode 100644
index 00000000..d169ac4d
--- /dev/null
+++ b/gmp/mpz/clrbit.c
@@ -0,0 +1,113 @@
+/* mpz_clrbit -- clear a specified bit.
+
+Copyright 1991, 1993, 1994, 1995, 2001, 2002 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 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 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 Lesser General Public
+License for more details.
+
+You should have received a copy of the GNU Lesser General Public License
+along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */
+
+#include "gmp.h"
+#include "gmp-impl.h"
+
+void
+mpz_clrbit (mpz_ptr d, unsigned long int bit_index)
+{
+  mp_size_t dsize = d->_mp_size;
+  mp_ptr dp = d->_mp_d;
+  mp_size_t limb_index;
+
+  limb_index = bit_index / GMP_NUMB_BITS;
+  if (dsize >= 0)
+    {
+      if (limb_index < dsize)
+	{
+          mp_limb_t  dlimb;
+          dlimb = dp[limb_index];
+          dlimb &= ~((mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS));
+          dp[limb_index] = dlimb;
+
+          if (UNLIKELY (dlimb == 0 && limb_index == dsize-1))
+            {
+              /* high limb became zero, must normalize */
+              do {
+                dsize--;
+              } while (dsize > 0 && dp[dsize-1] == 0);
+              d->_mp_size = dsize;
+            }
+	}
+      else
+	;
+    }
+  else
+    {
+      mp_size_t zero_bound;
+
+      /* Simulate two's complement arithmetic, i.e. simulate
+	 1. Set OP = ~(OP - 1) [with infinitely many leading ones].
+	 2. clear the bit.
+	 3. Set OP = ~OP + 1.  */
+
+      dsize = -dsize;
+
+      /* No upper bound on this loop, we're sure there's a non-zero limb
+	 sooner ot later.  */
+      for (zero_bound = 0; ; zero_bound++)
+	if (dp[zero_bound] != 0)
+	  break;
+
+      if (limb_index > zero_bound)
+	{
+	  if (limb_index < dsize)
+	    dp[limb_index] |= (mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS);
+	  else
+	    {
+	      /* Ugh.  The bit should be cleared outside of the end of the
+		 number.  We have to increase the size of the number.  */
+	      if (UNLIKELY (d->_mp_alloc < limb_index + 1))
+                dp = _mpz_realloc (d, limb_index + 1);
+
+	      MPN_ZERO (dp + dsize, limb_index - dsize);
+	      dp[limb_index] = (mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS);
+	      d->_mp_size = -(limb_index + 1);
+	    }
+	}
+      else if (limb_index == zero_bound)
+	{
+	  dp[limb_index] = ((((dp[limb_index] - 1)
+			      | ((mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS))) + 1)
+			    & GMP_NUMB_MASK);
+	  if (dp[limb_index] == 0)
+	    {
+	      mp_size_t i;
+	      for (i = limb_index + 1; i < dsize; i++)
+		{
+		  dp[i] = (dp[i] + 1) & GMP_NUMB_MASK;
+		  if (dp[i] != 0)
+		    goto fin;
+		}
+	      /* We got carry all way out beyond the end of D.  Increase
+		 its size (and allocation if necessary).  */
+	      dsize++;
+	      if (UNLIKELY (d->_mp_alloc < dsize))
+                dp = _mpz_realloc (d, dsize);
+
+	      dp[i] = 1;
+	      d->_mp_size = -dsize;
+	    fin:;
+	    }
+	}
+      else
+	;
+    }
+}