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/*=============================================================================
This file is part of FLINT.
FLINT 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 2 of the License, or
(at your option) any later version.
FLINT 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 FLINT; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
=============================================================================*/
/******************************************************************************
Copyright (C) 2011 William Hart
******************************************************************************/
#include <stdlib.h>
#include <gmp.h>
#include "flint.h"
#include "nmod_vec.h"
#include "nmod_poly.h"
#include "ulong_extras.h"
void
_nmod_poly_div_basecase_1(mp_ptr Q, mp_ptr W,
mp_srcptr A, slong A_len, mp_srcptr B, slong B_len,
nmod_t mod)
{
mp_limb_t lead_inv = n_invmod(B[B_len - 1], mod.n);
slong len, coeff = A_len - B_len;
mp_ptr R1 = W;
mp_srcptr Btop = B + B_len - 1;
flint_mpn_copyi(R1, A + B_len - 1, A_len - B_len + 1);
while (coeff >= 0)
{
R1[coeff] = n_mod2_preinv(R1[coeff], mod.n, mod.ninv);
while (coeff >= 0 && R1[coeff] == WORD(0))
{
Q[coeff--] = WORD(0);
if (coeff >= 0)
R1[coeff] = n_mod2_preinv(R1[coeff], mod.n, mod.ninv);
}
if (coeff >= 0)
{
mp_limb_t c, * R_sub;
Q[coeff] =
n_mulmod2_preinv(R1[coeff], lead_inv, mod.n, mod.ninv);
c = n_negmod(Q[coeff], mod.n);
len = FLINT_MIN(B_len - 1, coeff);
R_sub = R1 + coeff - len;
if (len > 0)
mpn_addmul_1(R_sub, Btop - len, len, c);
coeff--;
}
}
}
void
_nmod_poly_div_basecase_2(mp_ptr Q, mp_ptr W,
mp_srcptr A, slong A_len, mp_srcptr B, slong B_len,
nmod_t mod)
{
slong coeff, i, len;
mp_limb_t lead_inv = n_invmod(B[B_len - 1], mod.n);
mp_ptr B2, R2;
mp_srcptr Btop;
B2 = W;
for (i = 0; i < B_len - 1; i++)
{
B2[2 * i] = B[i];
B2[2 * i + 1] = 0;
}
Btop = B2 + 2*(B_len - 1);
R2 = W + 2*(B_len - 1);
for (i = 0; i < A_len - B_len + 1; i++)
{
R2[2 * i] = A[B_len + i - 1];
R2[2 * i + 1] = 0;
}
coeff = A_len - B_len;
while (coeff >= 0)
{
mp_limb_t r_coeff;
r_coeff =
n_ll_mod_preinv(R2[2 * coeff + 1], R2[2 * coeff], mod.n, mod.ninv);
while (coeff >= 0 && r_coeff == WORD(0))
{
Q[coeff--] = WORD(0);
if (coeff >= 0)
r_coeff =
n_ll_mod_preinv(R2[2 * coeff + 1], R2[2 * coeff], mod.n,
mod.ninv);
}
if (coeff >= 0)
{
mp_limb_t c, * R_sub;
Q[coeff] =
n_mulmod2_preinv(r_coeff, lead_inv, mod.n, mod.ninv);
c = n_negmod(Q[coeff], mod.n);
len = FLINT_MIN(B_len - 1, coeff);
R_sub = R2 + 2 * (coeff - len);
if (len > 0)
mpn_addmul_1(R_sub, Btop - 2*len, 2 * len, c);
coeff--;
}
}
}
void
_nmod_poly_div_basecase_3(mp_ptr Q, mp_ptr W,
mp_srcptr A, slong A_len, mp_srcptr B, slong B_len,
nmod_t mod)
{
slong coeff, i, len;
mp_limb_t lead_inv = n_invmod(B[B_len - 1], mod.n);
mp_limb_t r_coeff;
mp_ptr B3, R3;
mp_srcptr Btop;
B3 = W;
for (i = 0; i < B_len - 1; i++)
{
B3[3 * i] = B[i];
B3[3 * i + 1] = 0;
B3[3 * i + 2] = 0;
}
Btop = B3 + 3*(B_len - 1);
R3 = W + 3*(B_len - 1);
for (i = 0; i < A_len - B_len + 1; i++)
{
R3[3 * i] = A[B_len + i - 1];
R3[3 * i + 1] = 0;
R3[3 * i + 2] = 0;
}
coeff = A_len - B_len;
while (coeff >= 0)
{
r_coeff =
n_lll_mod_preinv(R3[3 * coeff + 2], R3[3 * coeff + 1],
R3[3 * coeff], mod.n, mod.ninv);
while (coeff >= 0 && r_coeff == WORD(0))
{
Q[coeff--] = WORD(0);
if (coeff >= 0)
r_coeff =
n_lll_mod_preinv(R3[3 * coeff + 2], R3[3 * coeff + 1],
R3[3 * coeff], mod.n, mod.ninv);
}
if (coeff >= 0)
{
mp_limb_t c, * R_sub;
Q[coeff] =
n_mulmod2_preinv(r_coeff, lead_inv, mod.n, mod.ninv);
c = n_negmod(Q[coeff], mod.n);
len = FLINT_MIN(B_len - 1, coeff);
R_sub = R3 + 3 * (coeff - len);
if (len > 0)
mpn_addmul_1(R_sub, Btop - 3*len, 3 * len, c);
coeff--;
}
}
}
void
_nmod_poly_div_basecase(mp_ptr Q, mp_ptr W,
mp_srcptr A, slong A_len, mp_srcptr B, slong B_len,
nmod_t mod)
{
slong bits =
2 * (FLINT_BITS - mod.norm) + FLINT_BIT_COUNT(A_len - B_len + 1);
if (bits <= FLINT_BITS)
_nmod_poly_div_basecase_1(Q, W, A, A_len, B, B_len, mod);
else if (bits <= 2 * FLINT_BITS)
_nmod_poly_div_basecase_2(Q, W, A, A_len, B, B_len, mod);
else
_nmod_poly_div_basecase_3(Q, W, A, A_len, B, B_len, mod);
}
void
nmod_poly_div_basecase(nmod_poly_t Q, const nmod_poly_t A,
const nmod_poly_t B)
{
mp_ptr Q_coeffs, W;
nmod_poly_t t1;
slong Alen, Blen;
TMP_INIT;
Blen = B->length;
if (Blen == 0)
{
flint_printf("Exception (nmod_poly_div_base). Division by zero.\n");
abort();
}
Alen = A->length;
if (Alen < Blen)
{
nmod_poly_zero(Q);
return;
}
if (Q == A || Q == B)
{
nmod_poly_init2_preinv(t1, B->mod.n, B->mod.ninv,
Alen - Blen + 1);
Q_coeffs = t1->coeffs;
}
else
{
nmod_poly_fit_length(Q, Alen - Blen + 1);
Q_coeffs = Q->coeffs;
}
TMP_START;
W = TMP_ALLOC(NMOD_DIV_BC_ITCH(Alen, Blen, A->mod)*sizeof(mp_limb_t));
_nmod_poly_div_basecase(Q_coeffs, W, A->coeffs, Alen,
B->coeffs, Blen, B->mod);
if (Q == A || Q == B)
{
nmod_poly_swap(Q, t1);
nmod_poly_clear(t1);
}
Q->length = Alen - Blen + 1;
TMP_END;
_nmod_poly_normalise(Q);
}
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