96 lines
2.1 KiB
C
96 lines
2.1 KiB
C
/*
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Copyright 2009 Jason Moxham
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This file is part of the MPIR Library.
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The MPIR 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
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by the Free Software Foundation; either version 2.1 of the License, or (at
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your option) any later version.
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The MPIR 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 MPIR Library; see the file COPYING.LIB. If not, write
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to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
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Boston, MA 02110-1301, USA.
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*/
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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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/*
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using a two limb inverse of a one limb divisor
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(xp, n) = (qp, n)*d - ret*B^n and 0 <= ret < d
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*/
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mp_limb_t mpn_divrem_hensel_qr_1_2(mp_ptr qp, mp_srcptr xp, mp_size_t n, mp_limb_t d)
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{
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mp_size_t j;
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mp_limb_t c, h, q, dummy, h1, t, ml, mh, xl, xh, ql, qh;
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ASSERT(n >= 2);
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ASSERT_MPN(xp, n);
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ASSERT(MPN_SAME_OR_SEPARATE_P(qp, xp, n));
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ASSERT(d%2 == 1);
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modlimb_invert(ml, d);
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umul_ppmm(h, dummy, d, ml);
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ASSERT(dummy == 1);
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h = -h;
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mh = ml*h; /* (mh, ml) is our two limb inverse */
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c = 0;
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h = 0;
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for (j = 0; j + 1 <= n - 1; j += 2)
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{
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xl = xp[j];
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xh = xp[j + 1];
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t = h + c;
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if (xh == 0 && t > xl) c = 1;
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else c = 0;
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sub_ddmmss(xh, xl, xh, xl, 0, t);
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umul_ppmm(qh, ql, xl, ml);
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qh = qh + xh*ml + xl*mh;
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qp[j] = ql;
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qp[j + 1] = qh;
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umul_ppmm(h, h1, qh, d);
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if (h1 > xh)
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h++;
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}
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if (j <= n - 1)
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{
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h1 = xp[j];
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t = h + c;
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if (t > h1)
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{
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h1 = h1 - t;
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c = 1;
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}
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else
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{
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h1 = h1 - t;
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c = 0;
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}
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q = h1*ml;
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qp[j] = q;
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umul_ppmm(h, dummy, q, d);
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ASSERT(dummy == h1);
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}
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return h + c;
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}
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