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132 lines
3.1 KiB
C
132 lines
3.1 KiB
C
/* mpn_gcd_22 -- double limb greatest common divisor.
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Copyright 1994, 1996, 2000, 2001, 2009, 2012, 2019 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 either:
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* the GNU Lesser General Public License as published by the Free
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Software Foundation; either version 3 of the License, or (at your
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option) any later version.
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or
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* the GNU General Public License as published by the Free Software
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Foundation; either version 2 of the License, or (at your option) any
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later version.
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or both in parallel, as here.
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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 General Public License
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for more details.
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You should have received copies of the GNU General Public License and the
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GNU Lesser General Public License along with the GNU MP Library. If not,
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see https://www.gnu.org/licenses/. */
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#include "gmp-impl.h"
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#include "longlong.h"
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#if GMP_NAIL_BITS > 0
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#error Nails not supported.
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#endif
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mp_double_limb_t
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mpn_gcd_22 (mp_limb_t u1, mp_limb_t u0, mp_limb_t v1, mp_limb_t v0)
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{
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mp_double_limb_t g;
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ASSERT (u0 & v0 & 1);
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/* Implicit least significant bit */
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u0 = (u0 >> 1) | (u1 << (GMP_LIMB_BITS - 1));
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u1 >>= 1;
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v0 = (v0 >> 1) | (v1 << (GMP_LIMB_BITS - 1));
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v1 >>= 1;
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while (u1 || v1) /* u1 == 0 can happen at most twice per call */
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{
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mp_limb_t vgtu, t1, t0;
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sub_ddmmss (t1, t0, u1, u0, v1, v0);
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vgtu = LIMB_HIGHBIT_TO_MASK(t1);
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if (UNLIKELY (t0 == 0))
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{
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if (t1 == 0)
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{
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g.d1 = (u1 << 1) | (u0 >> (GMP_LIMB_BITS - 1));
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g.d0 = (u0 << 1) | 1;
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return g;
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}
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int c;
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count_trailing_zeros (c, t1);
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/* v1 = min (u1, v1) */
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v1 += (vgtu & t1);
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/* u0 = |u1 - v1| */
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u0 = (t1 ^ vgtu) - vgtu;
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ASSERT (c < GMP_LIMB_BITS - 1);
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u0 >>= c + 1;
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u1 = 0;
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}
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else
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{
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int c;
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count_trailing_zeros (c, t0);
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c++;
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/* V <-- min (U, V).
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Assembly version should use cmov. Another alternative,
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avoiding carry propagation, would be
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v0 += vgtu & t0; v1 += vtgu & (u1 - v1);
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*/
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add_ssaaaa (v1, v0, v1, v0, vgtu & t1, vgtu & t0);
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/* U <-- |U - V|
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No carry handling needed in this conditional negation,
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since t0 != 0. */
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u0 = (t0 ^ vgtu) - vgtu;
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u1 = t1 ^ vgtu;
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if (UNLIKELY (c == GMP_LIMB_BITS))
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{
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u0 = u1;
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u1 = 0;
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}
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else
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{
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u0 = (u0 >> c) | (u1 << (GMP_LIMB_BITS - c));
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u1 >>= c;
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}
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}
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}
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while ((v0 | u0) & GMP_LIMB_HIGHBIT)
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{ /* At most two iterations */
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mp_limb_t vgtu, t0;
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int c;
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sub_ddmmss (vgtu, t0, 0, u0, 0, v0);
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if (UNLIKELY (t0 == 0))
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{
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g.d1 = u0 >> (GMP_LIMB_BITS - 1);
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g.d0 = (u0 << 1) | 1;
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return g;
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}
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/* v <-- min (u, v) */
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v0 += (vgtu & t0);
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/* u <-- |u - v| */
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u0 = (t0 ^ vgtu) - vgtu;
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count_trailing_zeros (c, t0);
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u0 = (u0 >> 1) >> c;
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}
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g.d0 = mpn_gcd_11 ((u0 << 1) + 1, (v0 << 1) + 1);
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g.d1 = 0;
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return g;
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}
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