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diff --git a/gmp/mpf/div_2exp.c b/gmp/mpf/div_2exp.c
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+/* mpf_div_2exp -- Divide a float by 2^n.
+
+Copyright 1993, 1994, 1996, 2000, 2001, 2002, 2004 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"
+
+
+/* Multiples of GMP_NUMB_BITS in exp simply mean an amount subtracted from
+   EXP(u) to set EXP(r).  The remainder exp%GMP_NUMB_BITS is then a right
+   shift for the limb data.
+
+   If exp%GMP_NUMB_BITS == 0 then there's no shifting, we effectively just
+   do an mpz_set with changed EXP(r).  Like mpz_set we take prec+1 limbs in
+   this case.  Although just prec would suffice, it's nice to have
+   mpf_div_2exp with exp==0 come out the same as mpz_set.
+
+   When shifting we take up to prec many limbs from the input.  Our shift is
+   cy = mpn_rshift (PTR(r)+1, PTR(u)+k, ...), where k is the number of low
+   limbs dropped from u, and the carry out is stored to PTR(r)[0].  We don't
+   try to work extra bits from PTR(u)[k-1] (when k>=1 makes it available)
+   into that low carry limb.  Just prec limbs (with the high non-zero) from
+   the input is enough bits for the application requested precision, no need
+   to do extra work.
+
+   If r==u the shift will have overlapping operands.  When k>=1 (ie. when
+   usize > prec), the overlap is in the style supported by rshift (ie. dst
+   <= src).
+
+   But when r==u and k==0 (ie. usize <= prec), we would have an invalid
+   overlap (mpn_rshift (rp+1, rp, ...)).  In this case we must instead use
+   mpn_lshift (PTR(r), PTR(u), size, NUMB-shift).  An lshift by NUMB-shift
+   bits gives identical data of course, it's just its overlap restrictions
+   which differ.
+
+   In both shift cases, the resulting data is abs_usize+1 limbs.  "adj" is
+   used to add +1 to that size if the high is non-zero (it may of course
+   have become zero by the shifting).  EXP(u) is the exponent just above
+   those abs_usize+1 limbs, so it gets -1+adj, which means -1 if the high is
+   zero, or no change if the high is non-zero.
+
+   Enhancements:
+
+   The way mpn_lshift is used means successive mpf_div_2exp calls on the
+   same operand will accumulate low zero limbs, until prec+1 limbs is
+   reached.  This is wasteful for subsequent operations.  When abs_usize <=
+   prec, we should test the low exp%GMP_NUMB_BITS many bits of PTR(u)[0],
+   ie. those which would be shifted out by an mpn_rshift.  If they're zero
+   then use that mpn_rshift.  */
+
+void
+mpf_div_2exp (mpf_ptr r, mpf_srcptr u, unsigned long int exp)
+{
+  mp_srcptr up;
+  mp_ptr rp = r->_mp_d;
+  mp_size_t usize;
+  mp_size_t abs_usize;
+  mp_size_t prec = r->_mp_prec;
+  mp_exp_t uexp = u->_mp_exp;
+
+  usize = u->_mp_size;
+
+  if (UNLIKELY (usize == 0))
+    {
+      r->_mp_size = 0;
+      r->_mp_exp = 0;
+      return;
+    }
+
+  abs_usize = ABS (usize);
+  up = u->_mp_d;
+
+  if (exp % GMP_NUMB_BITS == 0)
+    {
+      prec++;			/* retain more precision here as we don't need
+				   to account for carry-out here */
+      if (abs_usize > prec)
+	{
+	  up += abs_usize - prec;
+	  abs_usize = prec;
+	}
+      if (rp != up)
+	MPN_COPY_INCR (rp, up, abs_usize);
+      r->_mp_exp = uexp - exp / GMP_NUMB_BITS;
+    }
+  else
+    {
+      mp_limb_t cy_limb;
+      mp_size_t adj;
+      if (abs_usize > prec)
+	{
+	  up += abs_usize - prec;
+	  abs_usize = prec;
+	  /* Use mpn_rshift since mpn_lshift operates downwards, and we
+	     therefore would clobber part of U before using that part, in case
+	     R is the same variable as U.  */
+	  cy_limb = mpn_rshift (rp + 1, up, abs_usize, exp % GMP_NUMB_BITS);
+	  rp[0] = cy_limb;
+	  adj = rp[abs_usize] != 0;
+	}
+      else
+	{
+	  cy_limb = mpn_lshift (rp, up, abs_usize,
+				GMP_NUMB_BITS - exp % GMP_NUMB_BITS);
+	  rp[abs_usize] = cy_limb;
+	  adj = cy_limb != 0;
+	}
+
+      abs_usize += adj;
+      r->_mp_exp = uexp - exp / GMP_NUMB_BITS - 1 + adj;
+    }
+  r->_mp_size = usize >= 0 ? abs_usize : -abs_usize;
+}