pqc/external/flint-2.4.3/mpn_extras/remove_2exp.c

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2014-05-18 22:03:37 +00:00
/*=============================================================================
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 <gmp.h>
#include "flint.h"
#include "mpn_extras.h"
mp_size_t flint_mpn_remove_2exp(mp_ptr x, mp_size_t xsize, mp_bitcnt_t *bits)
{
mp_size_t shift_limbs, reduced_size;
mp_bitcnt_t shift_bits;
*bits = mpn_scan1(x, 0);
if (*bits == 0)
return xsize;
shift_limbs = *bits / FLINT_BITS;
shift_bits = *bits % FLINT_BITS;
reduced_size = xsize - shift_limbs;
if (shift_bits)
{
mpn_rshift(x, x + shift_limbs, reduced_size, shift_bits);
if (x[reduced_size - 1] == 0)
reduced_size -= 1;
}
else
{
flint_mpn_copyi(x, x + shift_limbs, reduced_size);
}
return reduced_size;
}