--- /dev/null
+/* mpz_divexact_gcd -- exact division optimized for GCDs.
+
+ THE FUNCTIONS IN THIS FILE ARE FOR INTERNAL USE AND ARE ALMOST CERTAIN TO
+ BE SUBJECT TO INCOMPATIBLE CHANGES IN FUTURE GNU MP RELEASES.
+
+Copyright 2000, 2005 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"
+
+
+/* Set q to a/d, expecting d to be from a GCD and therefore usually small.
+
+ The distribution of GCDs of random numbers can be found in Knuth volume 2
+ section 4.5.2 theorem D.
+
+ GCD chance
+ 1 60.8%
+ 2^k 20.2% (1<=k<32)
+ 3*2^k 9.0% (1<=k<32)
+ other 10.1%
+
+ Only the low limb is examined for optimizations, since GCDs bigger than
+ 2^32 (or 2^64) will occur very infrequently.
+
+ Future: This could change to an mpn_divexact_gcd, possibly partly
+ inlined, if/when the relevant mpq functions change to an mpn based
+ implementation. */
+
+
+static void
+mpz_divexact_by3 (mpz_ptr q, mpz_srcptr a)
+{
+ mp_size_t size = SIZ(a);
+ if (size == 0)
+ {
+ SIZ(q) = 0;
+ return;
+ }
+ else
+ {
+ mp_size_t abs_size = ABS(size);
+ mp_ptr qp;
+
+ MPZ_REALLOC (q, abs_size);
+
+ qp = PTR(q);
+ mpn_divexact_by3 (qp, PTR(a), abs_size);
+
+ abs_size -= (qp[abs_size-1] == 0);
+ SIZ(q) = (size>0 ? abs_size : -abs_size);
+ }
+}
+
+void
+mpz_divexact_gcd (mpz_ptr q, mpz_srcptr a, mpz_srcptr d)
+{
+ ASSERT (mpz_sgn (d) > 0);
+
+ if (SIZ(d) == 1)
+ {
+ mp_limb_t dl = PTR(d)[0];
+ int twos;
+
+ if (dl == 1)
+ {
+ if (q != a)
+ mpz_set (q, a);
+ return;
+ }
+ if (dl == 3)
+ {
+ mpz_divexact_by3 (q, a);
+ return;
+ }
+
+ count_trailing_zeros (twos, dl);
+ dl >>= twos;
+
+ if (dl == 1)
+ {
+ mpz_tdiv_q_2exp (q, a, twos);
+ return;
+ }
+ if (dl == 3)
+ {
+ mpz_tdiv_q_2exp (q, a, twos);
+ mpz_divexact_by3 (q, q);
+ return;
+ }
+ }
+
+ mpz_divexact (q, a, d);
+}