81 lines
2.2 KiB
C
81 lines
2.2 KiB
C
/* mpn_mullow_n -- multiply two n-limb nunbers and return the low n limbs
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of their products.
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Copyright 2004, 2005 Free Software Foundation, Inc.
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Copyright 2009 Jason Moxham
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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 2.1 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; see the file COPYING.LIB. If not, write to
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the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
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MA 02110-1301, USA. */
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/* Copyright 2008 Complete rewrite Only the name is the same
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Note: sets 2n limbs
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*/
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#include "mpir.h"
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#include "gmp-impl.h"
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void
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mpn_mullow_n (mp_ptr rp, mp_srcptr xp, mp_srcptr yp, mp_size_t n)
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{
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mp_size_t m;
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ASSERT (n > 0);
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ASSERT_MPN (xp, n);
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ASSERT_MPN (yp, n);
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ASSERT (!MPN_OVERLAP_P (rp, 2 * n, xp, n));
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ASSERT (!MPN_OVERLAP_P (rp, 2 * n, yp, n));
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if (BELOW_THRESHOLD (n, MULLOW_BASECASE_THRESHOLD))
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{
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mpn_mul_basecase (rp, xp, n, yp, n);
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return;
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}
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if (BELOW_THRESHOLD (n, MULLOW_DC_THRESHOLD))
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{
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mpn_mullow_n_basecase (rp, xp, yp, n);
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return;
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}
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if (ABOVE_THRESHOLD (n, MULLOW_MUL_THRESHOLD))
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{
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mpn_mul_n (rp, xp, yp, n);
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return;
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}
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/* choose optimal m st n/2 <= m <= n, choosing m == n is same as above */
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m = n * 87 / 128;
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if (2 * m < n)
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m = n - n / 2;
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if (m > n)
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m = n;
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ASSERT (n / 2 <= m);
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ASSERT (m <= n);
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mpn_mul_n(rp, xp, yp, m);
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mpn_mullow_n(rp + 2 * m, xp, yp + m, n - m);
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mpn_add_n(rp + m, rp + m, rp + 2 * m, n - m);
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mpn_mullow_n(rp + 2 * m, xp + m, yp, n - m);
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mpn_add_n(rp + m, rp + m, rp + 2 * m, n - m);
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return;
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}
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