gcdext_subdiv_step.c
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上传日期:2022-08-06
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- /* gcdext_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, 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"
- /* 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,
- return the new size, and cofactors. */
- /* Temporary storage: Needs n limbs for the quotient, at qp. tp must
- point to an area large enough for the resulting cofactor, plus one
- limb extra. All in all, 2N + 1 if N is a bound for both inputs and
- outputs. */
- mp_size_t
- mpn_gcdext_subdiv_step (mp_ptr gp, mp_size_t *gn, mp_ptr up, mp_size_t *usizep,
- mp_ptr ap, mp_ptr bp, mp_size_t n,
- mp_ptr u0, mp_ptr u1, mp_size_t *unp,
- mp_ptr qp, mp_ptr tp)
- {
- mp_size_t an, bn, un;
- mp_size_t qn;
- mp_size_t u0n;
- int swapped;
- an = bn = n;
- ASSERT (an > 0);
- ASSERT (ap[an-1] > 0 || bp[an-1] > 0);
- MPN_NORMALIZE (ap, an);
- MPN_NORMALIZE (bp, bn);
- un = *unp;
- swapped = 0;
- if (UNLIKELY (an == 0))
- {
- return_b:
- MPN_COPY (gp, bp, bn);
- *gn = bn;
- MPN_NORMALIZE (u0, un);
- MPN_COPY (up, u0, un);
- *usizep = swapped ? un : -un;
- return 0;
- }
- else if (UNLIKELY (bn == 0))
- {
- MPN_COPY (gp, ap, an);
- *gn = an;
- MPN_NORMALIZE (u1, un);
- MPN_COPY (up, u1, un);
- *usizep = swapped ? -un : un;
- return 0;
- }
- /* Arrange so that a > b, subtract an -= bn, and maintain
- normalization. */
- if (an < bn)
- {
- MPN_PTR_SWAP (ap, an, bp, bn);
- MP_PTR_SWAP (u0, u1);
- swapped ^= 1;
- }
- else if (an == bn)
- {
- int c;
- MPN_CMP (c, ap, bp, an);
- if (UNLIKELY (c == 0))
- {
- MPN_COPY (gp, ap, an);
- *gn = an;
- /* Must return the smallest cofactor, +u1 or -u0 */
- MPN_CMP (c, u0, u1, un);
- ASSERT (c != 0 || (un == 1 && u0[0] == 1 && u1[0] == 1));
- if (c < 0)
- {
- MPN_NORMALIZE (u0, un);
- MPN_COPY (up, u0, un);
- swapped ^= 1;
- }
- else
- {
- MPN_NORMALIZE_NOT_ZERO (u1, un);
- MPN_COPY (up, u1, un);
- }
- *usizep = swapped ? -un : un;
- return 0;
- }
- else if (c < 0)
- {
- MP_PTR_SWAP (ap, bp);
- MP_PTR_SWAP (u0, u1);
- swapped ^= 1;
- }
- }
- /* Reduce a -= b, u1 += u0 */
- ASSERT_NOCARRY (mpn_sub (ap, ap, an, bp, bn));
- MPN_NORMALIZE (ap, an);
- ASSERT (an > 0);
- u1[un] = mpn_add_n (u1, u1, u0, un);
- un += (u1[un] > 0);
- /* Arrange so that a > b, and divide a = q b + r */
- if (an < bn)
- {
- MPN_PTR_SWAP (ap, an, bp, bn);
- MP_PTR_SWAP (u0, u1);
- swapped ^= 1;
- }
- else if (an == bn)
- {
- int c;
- MPN_CMP (c, ap, bp, an);
- if (UNLIKELY (c == 0))
- goto return_b;
- else if (c < 0)
- {
- MP_PTR_SWAP (ap, bp);
- MP_PTR_SWAP (u0, u1);
- swapped ^= 1;
- }
- }
- /* Reduce a -= q b, u1 += q u0 */
- qn = an - bn + 1;
- mpn_tdiv_qr (qp, ap, 0, ap, an, bp, bn);
- if (mpn_zero_p (ap, bn))
- goto return_b;
- n = bn;
- /* Update u1 += q u0 */
- u0n = un;
- MPN_NORMALIZE (u0, u0n);
- if (u0n > 0)
- {
- qn -= (qp[qn - 1] == 0);
- if (qn > u0n)
- mpn_mul (tp, qp, qn, u0, u0n);
- else
- mpn_mul (tp, u0, u0n, qp, qn);
- if (qn + u0n > un)
- {
- ASSERT_NOCARRY (mpn_add (u1, tp, qn + u0n, u1, un));
- un = qn + u0n;
- un -= (u1[un-1] == 0);
- }
- else
- {
- u1[un] = mpn_add (u1, u1, un, tp, qn + u0n);
- un += (u1[un] > 0);
- }
- }
- *unp = un;
- return n;
- }