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diff --git a/mpz/pprime_p.c b/mpz/pprime_p.c
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+/* mpz_probab_prime_p --
+   An implementation of the probabilistic primality test found in Knuth's
+   Seminumerical Algorithms book.  If the function mpz_probab_prime_p()
+   returns 0 then n is not prime.  If it returns 1, then n is 'probably'
+   prime.  The probability of a false positive is (1/4)**reps, where
+   reps is the number of internal passes of the probabilistic algorithm.
+   Knuth indicates that 25 passes are reasonable.
+
+Copyright (C) 1991, 1993, 1994 Free Software Foundation, Inc.
+Contributed by John Amanatides.
+
+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"
+
+static int
+possibly_prime (n, n_minus_1, x, y, q, k)
+     mpz_srcptr n;
+     mpz_srcptr n_minus_1;
+     mpz_ptr x;
+     mpz_ptr y;
+     mpz_srcptr q;
+     unsigned long int k;
+{
+  unsigned long int i;
+
+  /* find random x s.t. 1 < x < n */
+  do
+    {
+      mpz_random (x, mpz_size (n));
+      mpz_mmod (x, x, n);
+    }
+  while (mpz_cmp_ui (x, 1L) <= 0);
+
+  mpz_powm (y, x, q, n);
+
+  if (mpz_cmp_ui (y, 1L) == 0 || mpz_cmp (y, n_minus_1) == 0)
+    return 1;
+
+  for (i = 1; i < k; i++)
+    {
+      mpz_powm_ui (y, y, 2L, n);
+      if (mpz_cmp (y, n_minus_1) == 0)
+	return 1;
+      if (mpz_cmp_ui (y, 1L) == 0)
+	return 0;
+    }
+  return 0;
+}
+
+int
+#if __STDC__
+mpz_probab_prime_p (mpz_srcptr m, int reps)
+#else
+mpz_probab_prime_p (m, reps)
+     mpz_srcptr m;
+     int reps;
+#endif
+{
+  mpz_t n, n_minus_1, x, y, q;
+  int i, is_prime;
+  unsigned long int k;
+
+  mpz_init (n);
+  /* Take the absolute value of M, to handle positive and negative primes.  */
+  mpz_abs (n, m);
+
+  if (mpz_cmp_ui (n, 3L) <= 0)
+    {
+      mpz_clear (n);
+      return mpz_cmp_ui (n, 1L) > 0;
+    }
+
+  if ((mpz_get_ui (n) & 1) == 0)
+    {
+      mpz_clear (n);
+      return 0;			/* even */
+    }
+
+  mpz_init (n_minus_1);
+  mpz_sub_ui (n_minus_1, n, 1L);
+  mpz_init (x);
+  mpz_init (y);
+
+  /* find q and k, s.t.  n = 1 + 2**k * q */
+  mpz_init_set (q, n_minus_1);
+  k = mpz_scan1 (q, 0);
+  mpz_tdiv_q_2exp (q, q, k);
+
+  is_prime = 1;
+  for (i = 0; i < reps && is_prime; i++)
+    is_prime &= possibly_prime (n, n_minus_1, x, y, q, k);
+
+  mpz_clear (n_minus_1);
+  mpz_clear (n);
+  mpz_clear (x);
+  mpz_clear (y);
+  mpz_clear (q);
+  return is_prime;
+}