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diff --git a/gmp/mpn/generic/mod_1_1.c b/gmp/mpn/generic/mod_1_1.c
new file mode 100644
index 00000000..27c7f8f1
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+++ b/gmp/mpn/generic/mod_1_1.c
@@ -0,0 +1,104 @@
+/* mpn_mod_1s_1p (ap, n, b, cps)
+   Divide (ap,,n) by b.  Return the single-limb remainder.
+   Requires that b < B / 2.
+
+   Contributed to the GNU project by Torbjorn Granlund.
+
+   THE FUNCTIONS IN THIS FILE ARE INTERNAL WITH MUTABLE INTERFACES.  IT IS ONLY
+   SAFE TO REACH THEM THROUGH DOCUMENTED INTERFACES.  IN FACT, IT IS ALMOST
+   GUARANTEED THAT THEY WILL CHANGE OR DISAPPEAR IN A FUTURE GNU MP RELEASE.
+
+Copyright 2008, 2009 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"
+#include "longlong.h"
+
+void
+mpn_mod_1s_1p_cps (mp_limb_t cps[4], mp_limb_t b)
+{
+  mp_limb_t bi;
+  mp_limb_t B1modb, B2modb;
+  int cnt;
+
+  ASSERT (b <= GMP_NUMB_MAX / 2);
+
+  count_leading_zeros (cnt, b);
+
+  b <<= cnt;
+  invert_limb (bi, b);
+
+  B1modb = -b * ((bi >> (GMP_LIMB_BITS-cnt)) | (CNST_LIMB(1) << cnt));
+  ASSERT (B1modb <= b);		/* NB: not fully reduced mod b */
+  udiv_rnd_preinv (B2modb, B1modb, b, bi);
+
+  B1modb >>= cnt;
+  B2modb >>= cnt;
+
+  cps[0] = bi;
+  cps[1] = cnt;
+  cps[2] = B1modb;
+  cps[3] = B2modb;
+}
+
+mp_limb_t
+mpn_mod_1s_1p (mp_srcptr ap, mp_size_t n, mp_limb_t b, mp_limb_t bmodb[4])
+{
+  mp_limb_t rh, rl, bi, q, ph, pl, r;
+  mp_limb_t B1modb, B2modb;
+  mp_size_t i;
+  int cnt;
+
+  B1modb = bmodb[2];
+  B2modb = bmodb[3];
+
+  umul_ppmm (ph, pl, ap[n - 1], B1modb);
+  add_ssaaaa (rh, rl, ph, pl, 0, ap[n - 2]);
+
+  for (i = n - 3; i >= 0; i -= 1)
+    {
+      /* rr = ap[i]				< B
+	    + LO(rr)  * (B mod b)		<= (B-1)(b-1)
+	    + HI(rr)  * (B^2 mod b)		<= (B-1)(b-1)
+      */
+      umul_ppmm (ph, pl, rl, B1modb);
+      add_ssaaaa (ph, pl, ph, pl, 0, ap[i]);
+
+      umul_ppmm (rh, rl, rh, B2modb);
+      add_ssaaaa (rh, rl, rh, rl, ph, pl);
+    }
+
+  bi = bmodb[0];
+  cnt = bmodb[1];
+#if 1
+  {
+    mp_limb_t mask;
+    r = (rh << cnt) | (rl >> (GMP_LIMB_BITS - cnt));
+    mask = -(mp_limb_t) (r >= b);
+    r -= mask & b;
+  }
+#else
+  udiv_qrnnd_preinv (q, r, rh >> (GMP_LIMB_BITS - cnt),
+		     (rh << cnt) | (rl >> (GMP_LIMB_BITS - cnt)), b, bi);
+  ASSERT (q <= 1);	/* optimize for small quotient? */
+#endif
+
+  udiv_qrnnd_preinv (q, r, r, rl << cnt, b, bi);
+
+  return r >> cnt;
+}