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/* mpn_dc_div_qr -- recursive divide-and-conquer division for arbitrary size
operands.
Contributed to the GNU project by Torbjörn Granlund.
THE FUNCTIONS IN THIS FILE ARE INTERNAL WITH A MUTABLE INTERFACE. IT IS
ONLY SAFE TO REACH THEM THROUGH DOCUMENTED INTERFACES. IN FACT, IT IS
ALMOST GUARANTEED THAT THEY WILL CHANGE OR DISAPPEAR IN A FUTURE GMP
RELEASE.
Copyright 2006, 2007 Free Software Foundation, Inc.
This file is part of the GNU MP Library.
The GNU MP Library is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the Free
Software Foundation; either version 3 of the License, or (at your option) any
later version.
The GNU MP Library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
details.
You should have received a copy of the GNU General Public License along with
the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
#include "gmp.h"
#include "gmp-impl.h"
mp_limb_t
mpn_dc_div_qr_n (mp_ptr qp, mp_ptr np, mp_srcptr dp, mp_size_t n,
mp_srcptr dip, mp_ptr tp)
{
mp_size_t lo, hi;
mp_limb_t cy, qh, ql;
lo = n >> 1; /* floor(n/2) */
hi = n - lo; /* ceil(n/2) */
if (BELOW_THRESHOLD (hi, DC_DIV_QR_THRESHOLD))
qh = mpn_sb_div_qr (qp + lo, np + 2 * lo, 2 * hi, dp + lo, hi, dip);
else
qh = mpn_dc_div_qr_n (qp + lo, np + 2 * lo, dp + lo, hi, dip, tp);
mpn_mul (tp, qp + lo, hi, dp, lo);
cy = mpn_sub_n (np + lo, np + lo, tp, n);
if (qh != 0)
cy += mpn_sub_n (np + n, np + n, dp, lo);
while (cy != 0)
{
qh -= mpn_sub_1 (qp + lo, qp + lo, hi, 1);
cy -= mpn_add_n (np + lo, np + lo, dp, n);
}
if (BELOW_THRESHOLD (lo, DC_DIV_QR_THRESHOLD))
ql = mpn_sb_div_qr (qp, np + hi, 2 * lo, dp + hi, lo, dip);
else
ql = mpn_dc_div_qr_n (qp, np + hi, dp + hi, lo, dip, tp);
mpn_mul (tp, dp, hi, qp, lo);
cy = mpn_sub_n (np, np, tp, n);
if (ql != 0)
cy += mpn_sub_n (np + lo, np + lo, dp, hi);
while (cy != 0)
{
mpn_sub_1 (qp, qp, lo, 1);
cy -= mpn_add_n (np, np, dp, n);
}
return qh;
}
mp_limb_t
mpn_preinv_dc_div_qr (mp_ptr qp,
mp_ptr np, mp_size_t nn,
mp_srcptr dp, mp_size_t dn,
mp_srcptr dip)
{
mp_size_t qn;
mp_limb_t qh, cy;
mp_ptr tp;
TMP_DECL;
TMP_MARK;
tp = TMP_SALLOC_LIMBS (dn);
qn = nn - dn;
qp += qn;
np += nn;
dp += dn;
if (qn > dn)
{
/* Reduce qn mod dn without division, optimizing small operations. */
do
qn -= dn;
while (qn > dn);
qp -= qn; /* point at low limb of next quotient block */
np -= qn; /* point in the middle of partial remainder */
/* Perform the typically smaller block first. */
if (BELOW_THRESHOLD (qn, DC_DIV_QR_THRESHOLD))
qh = mpn_sb_div_qr (qp, np - qn, 2 * qn, dp - qn, qn, dip);
else
qh = mpn_dc_div_qr_n (qp, np - qn, dp - qn, qn, dip, tp);
if (qn != dn)
{
if (qn > dn - qn)
mpn_mul (tp, qp, qn, dp - dn, dn - qn);
else
mpn_mul (tp, dp - dn, dn - qn, qp, qn);
cy = mpn_sub_n (np - dn, np - dn, tp, dn);
if (qh != 0)
cy += mpn_sub_n (np - dn + qn, np - dn + qn, dp - dn, dn - qn);
while (cy != 0)
{
qh -= mpn_sub_1 (qp, qp, qn, 1);
cy -= mpn_add_n (np - dn, np - dn, dp - dn, dn);
}
}
qn = nn - dn - qn;
do
{
qp -= dn;
np -= dn;
mpn_dc_div_qr_n (qp, np - dn, dp - dn, dn, dip, tp);
qn -= dn;
}
while (qn > 0);
}
else
{
if (qn == 0)
{
qh = mpn_cmp (np - dn, dp - dn, dn) >= 0;
if (qh)
mpn_sub_n (np - dn, np - dn, dp - dn, dn);
TMP_FREE;
return qh;
}
qp -= qn; /* point at low limb of next quotient block */
np -= qn; /* point in the middle of partial remainder */
if (BELOW_THRESHOLD (qn, DC_DIV_QR_THRESHOLD))
qh = mpn_sb_div_qr (qp, np - qn, 2 * qn, dp - qn, qn, dip);
else
qh = mpn_dc_div_qr_n (qp, np - qn, dp - qn, qn, dip, tp);
if (qn != dn)
{
if (qn > dn - qn)
mpn_mul (tp, qp, qn, dp - dn, dn - qn);
else
mpn_mul (tp, dp - dn, dn - qn, qp, qn);
cy = mpn_sub_n (np - dn, np - dn, tp, dn);
if (qh != 0)
cy += mpn_sub_n (np - dn + qn, np - dn + qn, dp - dn, dn - qn);
while (cy != 0)
{
qh -= mpn_sub_1 (qp, qp, qn, 1);
cy -= mpn_add_n (np - dn, np - dn, dp - dn, dn);
}
}
}
TMP_FREE;
return qh;
}
mp_limb_t
mpn_dc_div_qr (mp_ptr qp, mp_ptr np, mp_size_t nn, mp_srcptr dp, mp_size_t dn)
{
mp_limb_t cy;
mp_limb_t xp[2], dip[2];
ASSERT (dn >= 2);
cy = mpn_add_1 (xp, dp + dn - 2, 2, 1);
if (cy != 0)
dip[0] = dip[1] = 0;
else
mpn_invert (dip, xp, 2);
return mpn_preinv_dc_div_qr (qp, np, nn, dp, dn, dip);
}
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