pqc/external/flint-2.4.3/fmpz_poly/pseudo_divrem_cohen.c
2014-05-24 23:16:06 +02:00

157 lines
4.2 KiB
C

/*=============================================================================
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) 2010 Sebastian Pancratz
******************************************************************************/
#include <stdlib.h>
#include <gmp.h>
#include "flint.h"
#include "fmpz.h"
#include "fmpz_vec.h"
#include "fmpz_poly.h"
void
_fmpz_poly_pseudo_divrem_cohen(fmpz * Q, fmpz * R, const fmpz * A,
slong lenA, const fmpz * B, slong lenB)
{
const fmpz * leadB = B + (lenB - 1);
slong e, lenQ;
fmpz_t pow;
if (lenB == 1)
{
fmpz_init(pow);
fmpz_pow_ui(pow, leadB, lenA - 1);
_fmpz_vec_scalar_mul_fmpz(Q, A, lenA, pow);
_fmpz_vec_zero(R, lenA);
fmpz_clear(pow);
return;
}
lenQ = lenA - lenB + 1;
_fmpz_vec_zero(Q, lenQ);
if (R != A)
_fmpz_vec_set(R, A, lenA);
e = lenA - lenB;
/* Unroll the first run of the while loop */
{
fmpz_set(Q + (lenQ - 1), R + (lenA - 1));
_fmpz_vec_scalar_mul_fmpz(R, R, lenA - 1, leadB);
_fmpz_vec_scalar_submul_fmpz(R + (lenA - lenB), B, lenB - 1, R + (lenA - 1));
fmpz_zero(R + (lenA - 1));
lenA--;
FMPZ_VEC_NORM(R, lenA);
}
while (lenA >= lenB)
{
_fmpz_vec_scalar_mul_fmpz(Q, Q, lenQ, leadB);
fmpz_add(Q + (lenA - lenB), Q + (lenA - lenB), R + (lenA - 1));
_fmpz_vec_scalar_mul_fmpz(R, R, lenA - 1, leadB);
_fmpz_vec_scalar_submul_fmpz(R + lenA - lenB, B, lenB - 1, R + (lenA - 1));
fmpz_zero(R + (lenA - 1));
lenA--;
FMPZ_VEC_NORM(R, lenA);
e--;
}
fmpz_init(pow);
fmpz_pow_ui(pow, leadB, e);
_fmpz_vec_scalar_mul_fmpz(Q, Q, lenQ, pow);
_fmpz_vec_scalar_mul_fmpz(R, R, lenA, pow);
fmpz_clear(pow);
}
void
fmpz_poly_pseudo_divrem_cohen(fmpz_poly_t Q, fmpz_poly_t R,
const fmpz_poly_t A, const fmpz_poly_t B)
{
slong lenq, lenr;
fmpz *q, *r;
if (B->length == 0)
{
flint_printf("Exception (fmpz_poly_pseudo_divrem_cohen). Division by zero.\n");
abort();
}
if (Q == R)
{
flint_printf("Exception (fmpz_poly_pseudo_divrem_cohen). \n"
"Output arguments Q and R may not be aliased.\n");
abort();
}
if (A->length < B->length)
{
fmpz_poly_zero(Q);
fmpz_poly_set(R, A);
return;
}
lenq = A->length - B->length + 1;
lenr = A->length;
if ((Q == A) || (Q == B))
q = _fmpz_vec_init(lenq);
else
{
fmpz_poly_fit_length(Q, lenq);
q = Q->coeffs;
}
if (R == B)
r = _fmpz_vec_init(lenr);
else
{
fmpz_poly_fit_length(R, lenr);
r = R->coeffs;
}
_fmpz_poly_pseudo_divrem_cohen(q, r, A->coeffs, A->length, B->coeffs, B->length);
for (lenr = B->length - 1; (lenr >= 0) && r[lenr] == WORD(0); lenr--) ;
lenr++;
if ((Q == A) || (Q == B))
{
_fmpz_vec_clear(Q->coeffs, Q->alloc);
Q->coeffs = q;
Q->alloc = lenq;
Q->length = lenq;
}
else
_fmpz_poly_set_length(Q, lenq);
if (R == B)
{
_fmpz_vec_clear(R->coeffs, R->alloc);
R->coeffs = r;
R->alloc = A->length;
R->length = lenr;
}
else
_fmpz_poly_set_length(R, lenr);
}