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diff --git a/gmp/mpn/generic/mod_34lsub1.c b/gmp/mpn/generic/mod_34lsub1.c
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+/* mpn_mod_34lsub1 -- remainder modulo 2^(GMP_NUMB_BITS*3/4)-1.
+
+   THE FUNCTIONS IN THIS FILE ARE FOR INTERNAL USE ONLY.  THEY'RE ALMOST
+   CERTAIN TO BE SUBJECT TO INCOMPATIBLE CHANGES OR DISAPPEAR COMPLETELY IN
+   FUTURE GNU MP RELEASES.
+
+Copyright 2000, 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"
+
+
+/* Calculate a remainder from {p,n} divided by 2^(GMP_NUMB_BITS*3/4)-1.
+   The remainder is not fully reduced, it's any limb value congruent to
+   {p,n} modulo that divisor.
+
+   This implementation is only correct when GMP_NUMB_BITS is a multiple of
+   4.
+
+   FIXME: If GMP_NAIL_BITS is some silly big value during development then
+   it's possible the carry accumulators c0,c1,c2 could overflow.
+
+   General notes:
+
+   The basic idea is to use a set of N accumulators (N=3 in this case) to
+   effectively get a remainder mod 2^(GMP_NUMB_BITS*N)-1 followed at the end
+   by a reduction to GMP_NUMB_BITS*N/M bits (M=4 in this case) for a
+   remainder mod 2^(GMP_NUMB_BITS*N/M)-1.  N and M are chosen to give a good
+   set of small prime factors in 2^(GMP_NUMB_BITS*N/M)-1.
+
+   N=3 M=4 suits GMP_NUMB_BITS==32 and GMP_NUMB_BITS==64 quite well, giving
+   a few more primes than a single accumulator N=1 does, and for no extra
+   cost (assuming the processor has a decent number of registers).
+
+   For strange nailified values of GMP_NUMB_BITS the idea would be to look
+   for what N and M give good primes.  With GMP_NUMB_BITS not a power of 2
+   the choices for M may be opened up a bit.  But such things are probably
+   best done in separate code, not grafted on here.  */
+
+#if GMP_NUMB_BITS % 4 == 0
+
+#define B1  (GMP_NUMB_BITS / 4)
+#define B2  (B1 * 2)
+#define B3  (B1 * 3)
+
+#define M1  ((CNST_LIMB(1) << B1) - 1)
+#define M2  ((CNST_LIMB(1) << B2) - 1)
+#define M3  ((CNST_LIMB(1) << B3) - 1)
+
+#define LOW0(n)      ((n) & M3)
+#define HIGH0(n)     ((n) >> B3)
+
+#define LOW1(n)      (((n) & M2) << B1)
+#define HIGH1(n)     ((n) >> B2)
+
+#define LOW2(n)      (((n) & M1) << B2)
+#define HIGH2(n)     ((n) >> B1)
+
+#define PARTS0(n)    (LOW0(n) + HIGH0(n))
+#define PARTS1(n)    (LOW1(n) + HIGH1(n))
+#define PARTS2(n)    (LOW2(n) + HIGH2(n))
+
+#define ADD(c,a,val)                    \
+  do {                                  \
+    mp_limb_t  new_c;                   \
+    ADDC_LIMB (new_c, a, a, val);       \
+    (c) += new_c;                       \
+  } while (0)
+
+mp_limb_t
+mpn_mod_34lsub1 (mp_srcptr p, mp_size_t n)
+{
+  mp_limb_t  c0 = 0;
+  mp_limb_t  c1 = 0;
+  mp_limb_t  c2 = 0;
+  mp_limb_t  a0, a1, a2;
+
+  ASSERT (n >= 1);
+  ASSERT (n/3 < GMP_NUMB_MAX);
+
+  a0 = a1 = a2 = 0;
+  c0 = c1 = c2 = 0;
+
+  while ((n -= 3) >= 0)
+    {
+      ADD (c0, a0, p[0]);
+      ADD (c1, a1, p[1]);
+      ADD (c2, a2, p[2]);
+      p += 3;
+    }
+
+  if (n != -3)
+    {
+      ADD (c0, a0, p[0]);
+      if (n != -2)
+	ADD (c1, a1, p[1]);
+    }
+
+  return
+    PARTS0 (a0) + PARTS1 (a1) + PARTS2 (a2)
+    + PARTS1 (c0) + PARTS2 (c1) + PARTS0 (c2);
+}
+
+#endif