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gcd_subdiv_step.c
Package: gmp-5.0.1.tar.gz [view]
Upload User: qaz666999
Upload Date: 2022-08-06
Package Size: 2570k
Code Size: 3k
Category:
Algorithm
Development Platform:
Unix_Linux
- /* gcd_subdiv_step.c.
- 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'LL CHANGE OR DISAPPEAR IN A FUTURE GNU MP RELEASE.
- Copyright 2003, 2004, 2005, 2008 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"
- /* Used when mpn_hgcd or mpn_hgcd2 has failed. Then either one of a or
- b is small, or the difference is small. Perform one subtraction
- followed by one division. If the gcd is found, stores it in gp and
- *gn, and returns zero. Otherwise, compute the reduced a and b, and
- return the new size. */
- /* FIXME: Check when the smaller number is a single limb, and invoke
- * mpn_gcd_1. */
- mp_size_t
- mpn_gcd_subdiv_step (mp_ptr gp, mp_size_t *gn,
- mp_ptr ap, mp_ptr bp, mp_size_t n, mp_ptr tp)
- {
- mp_size_t an, bn;
- ASSERT (n > 0);
- ASSERT (ap[n-1] > 0 || bp[n-1] > 0);
- an = bn = n;
- MPN_NORMALIZE (ap, an);
- MPN_NORMALIZE (bp, bn);
- if (UNLIKELY (an == 0))
- {
- return_b:
- MPN_COPY (gp, bp, bn);
- *gn = bn;
- return 0;
- }
- else if (UNLIKELY (bn == 0))
- {
- return_a:
- MPN_COPY (gp, ap, an);
- *gn = an;
- return 0;
- }
- /* Arrange so that a > b, subtract an -= bn, and maintain
- normalization. */
- if (an < bn)
- MPN_PTR_SWAP (ap, an, bp, bn);
- else if (an == bn)
- {
- int c;
- MPN_CMP (c, ap, bp, an);
- if (UNLIKELY (c == 0))
- goto return_a;
- else if (c < 0)
- MP_PTR_SWAP (ap, bp);
- }
- ASSERT_NOCARRY (mpn_sub (ap, ap, an, bp, bn));
- MPN_NORMALIZE (ap, an);
- ASSERT (an > 0);
- /* Arrange so that a > b, and divide a = q b + r */
- /* FIXME: an < bn happens when we have cancellation. If that is the
- common case, then we could reverse the roles of a and b to avoid
- the swap. */
- if (an < bn)
- MPN_PTR_SWAP (ap, an, bp, bn);
- else if (an == bn)
- {
- int c;
- MPN_CMP (c, ap, bp, an);
- if (UNLIKELY (c == 0))
- goto return_a;
- else if (c < 0)
- MP_PTR_SWAP (ap, bp);
- }
- mpn_tdiv_qr (tp, ap, 0, ap, an, bp, bn);
- if (mpn_zero_p (ap, bn))
- goto return_b;
- return bn;
- }