105 lines
2.9 KiB
C
105 lines
2.9 KiB
C
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/* gcd_subdiv_step.c.
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THE FUNCTIONS IN THIS FILE ARE INTERNAL WITH MUTABLE INTERFACES. IT IS ONLY
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SAFE TO REACH THEM THROUGH DOCUMENTED INTERFACES. IN FACT, IT IS ALMOST
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GUARANTEED THAT THEY'LL CHANGE OR DISAPPEAR IN A FUTURE GNU MP RELEASE.
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Copyright 2003, 2004, 2005, 2008 Free Software Foundation, Inc.
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This file is part of the GNU MP Library.
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The GNU MP Library is free software; you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 3 of the License, or (at your
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option) any later version.
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The GNU MP Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
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#include "mpir.h"
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#include "gmp-impl.h"
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#include "longlong.h"
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/* Used when mpn_hgcd or mpn_hgcd2 has failed. Then either one of a or
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b is small, or the difference is small. Perform one subtraction
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followed by one division. If the gcd is found, stores it in gp and
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*gn, and returns zero. Otherwise, compute the reduced a and b, and
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return the new size. */
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/* FIXME: Check when the smaller number is a single limb, and invoke
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* mpn_gcd_1. */
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mp_size_t
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mpn_gcd_subdiv_step (mp_ptr gp, mp_size_t *gn,
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mp_ptr ap, mp_ptr bp, mp_size_t n, mp_ptr tp)
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{
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mp_size_t an, bn;
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ASSERT (n > 0);
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ASSERT (ap[n-1] > 0 || bp[n-1] > 0);
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an = bn = n;
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MPN_NORMALIZE (ap, an);
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MPN_NORMALIZE (bp, bn);
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if (UNLIKELY (an == 0))
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{
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return_b:
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MPN_COPY (gp, bp, bn);
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*gn = bn;
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return 0;
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}
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else if (UNLIKELY (bn == 0))
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{
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return_a:
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MPN_COPY (gp, ap, an);
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*gn = an;
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return 0;
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}
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/* Arrange so that a > b, subtract an -= bn, and maintain
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normalization. */
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if (an < bn)
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MPN_PTR_SWAP (ap, an, bp, bn);
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else if (an == bn)
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{
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int c;
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MPN_CMP (c, ap, bp, an);
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if (UNLIKELY (c == 0))
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goto return_a;
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else if (c < 0)
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MP_PTR_SWAP (ap, bp);
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}
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ASSERT_NOCARRY (mpn_sub (ap, ap, an, bp, bn));
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MPN_NORMALIZE (ap, an);
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ASSERT (an > 0);
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/* Arrange so that a > b, and divide a = q b + r */
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/* FIXME: an < bn happens when we have cancellation. If that is the
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common case, then we could reverse the roles of a and b to avoid
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the swap. */
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if (an < bn)
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MPN_PTR_SWAP (ap, an, bp, bn);
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else if (an == bn)
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{
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int c;
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MPN_CMP (c, ap, bp, an);
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if (UNLIKELY (c == 0))
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goto return_a;
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else if (c < 0)
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MP_PTR_SWAP (ap, bp);
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}
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mpn_tdiv_qr (tp, ap, 0, ap, an, bp, bn);
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if (mpn_zero_p (ap, bn))
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goto return_b;
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return bn;
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}
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