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

108 lines
3.2 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 Fredrik Johansson
******************************************************************************/
#include <stdlib.h>
#include <gmp.h>
#include "flint.h"
#include "fmpz.h"
#include "mpn_extras.h"
mp_size_t flint_mpn_remove_power_ascending(mp_ptr x, mp_size_t xsize,
mp_ptr p, mp_size_t psize, ulong *exp)
{
int i, maxi;
mp_ptr div;
mp_ptr rem;
mp_ptr square[FLINT_BITS];
mp_size_t square_size[FLINT_BITS];
mp_size_t sqsize;
*exp = 0;
if (psize > xsize)
return xsize;
maxi = 0;
square[0] = p;
square_size[0] = psize;
/* Most likely less memory will be needed, but this way we
avoid reallocations */
div = flint_malloc(sizeof(mp_limb_t) * xsize);
rem = flint_malloc(sizeof(mp_limb_t) * xsize);
/* Remove ascending powers */
for (i = 0; i < FLINT_BITS && xsize >= square_size[i]; i++)
{
mpn_tdiv_qr(div, rem, 0, x, xsize, square[i], square_size[i]);
if (!flint_mpn_zero_p(rem, square_size[i]))
{
i -= 1;
break;
}
*exp += (1 << i);
xsize = xsize - square_size[i] + 1;
if (div[xsize-1] == 0)
xsize--;
flint_mpn_copyi(x, div, xsize);
/* Form next square if needed */
sqsize = square_size[i] * 2;
if (sqsize - 1 > xsize)
break;
maxi = i + 1;
square[i + 1] = flint_malloc(sizeof(mp_limb_t) * sqsize);
mpn_sqr(square[i + 1], square[i], square_size[i]);
if (square[i + 1][sqsize - 1] == 0)
sqsize -= 1;
square_size[i + 1] = sqsize;
}
/* Remove descending powers */
for ( ; i >= 0; i--)
{
if (xsize >= square_size[i])
{
mpn_tdiv_qr(div, rem, 0, x, xsize, square[i], square_size[i]);
if (flint_mpn_zero_p(rem, square_size[i]))
{
*exp += (1 << i);
xsize = xsize - square_size[i] + 1;
if (div[xsize-1] == 0)
xsize--;
flint_mpn_copyi(x, div, xsize);
}
}
}
for (i = 1; i <= maxi; i++)
flint_free(square[i]);
flint_free(div);
flint_free(rem);
return xsize;
}