102 lines
2.5 KiB
C
102 lines
2.5 KiB
C
/* mpn_sb_div_qr -- Schoolbook division using the Möller-Granlund 3/2
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division algorithm.
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Contributed to the GNU project by Torbjorn Granlund.
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THE FUNCTION IN THIS FILE IS INTERNAL WITH A MUTABLE INTERFACE. IT IS ONLY
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SAFE TO REACH IT THROUGH DOCUMENTED INTERFACES. IN FACT, IT IS ALMOST
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GUARANTEED THAT IT WILL CHANGE OR DISAPPEAR IN A FUTURE GMP RELEASE.
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Copyright 2007, 2009 Free Software Foundation, Inc.
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Copyright 2010 William Hart (minor modifications)
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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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mp_limb_t
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mpn_sb_div_qr (mp_ptr qp,
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mp_ptr np, mp_size_t nn,
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mp_srcptr dp, mp_size_t dn,
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mp_limb_t dinv)
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{
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mp_limb_t qh;
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mp_size_t i;
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mp_limb_t n1, n0;
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mp_limb_t d1, d0;
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mp_limb_t cy, cy1;
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mp_limb_t q;
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ASSERT (dn > 2);
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ASSERT (nn >= dn);
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ASSERT ((dp[dn-1] & GMP_NUMB_HIGHBIT) != 0);
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np += nn;
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qh = mpn_cmp (np - dn, dp, dn) >= 0;
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if (qh != 0)
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mpn_sub_n (np - dn, np - dn, dp, dn);
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qp += nn - dn;
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dn -= 2; /* offset dn by 2 for main division loops,
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saving two iterations in mpn_submul_1. */
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d1 = dp[dn + 1];
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d0 = dp[dn + 0];
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np -= 2;
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n1 = np[1];
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for (i = nn - (dn + 2); i > 0; i--)
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{
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np--;
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if (UNLIKELY (n1 == d1) && np[1] == d0)
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{
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q = GMP_NUMB_MASK;
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mpn_submul_1 (np - dn, dp, dn + 2, q);
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n1 = np[1]; /* update n1, last loop's value will now be invalid */
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}
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else
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{
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tdiv_qr_3by2 (q, n1, n0, n1, np[1], np[0], d1, d0, dinv);
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cy = mpn_submul_1 (np - dn, dp, dn, q);
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cy1 = n0 < cy;
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n0 = (n0 - cy) & GMP_NUMB_MASK;
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cy = n1 < cy1;
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n1 = (n1 - cy1) & GMP_NUMB_MASK;
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np[0] = n0;
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if (UNLIKELY (cy != 0))
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{
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n1 += d1 + mpn_add_n (np - dn, np - dn, dp, dn + 1);
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q--;
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}
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}
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*--qp = q;
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}
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np[1] = n1;
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return qh;
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}
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