pqc/external/flint-2.4.3/ulong_extras/remove.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) 2009 William Hart
******************************************************************************/
#include <gmp.h>
#include "flint.h"
#include "ulong_extras.h"
int
n_remove(mp_limb_t * n, mp_limb_t p)
{
int exp, i;
mp_limb_t powp[6];
mp_limb_t quot, rem;
if (p == 2)
{
count_trailing_zeros(exp, *n);
if (exp)
(*n) >>= exp;
return exp;
}
powp[0] = p;
for (i = 0; ; i++)
{
if ((*n) < powp[i])
break;
quot = (*n) / powp[i];
rem = (*n) - quot * powp[i];
if (rem != UWORD(0))
break;
powp[i + 1] = powp[i] * powp[i];
(*n) = quot;
}
exp = (1 << i) - 1;
while (i > 0)
{
i--;
if ((*n) < powp[i])
continue;
quot = (*n) / powp[i];
rem = (*n) - quot * powp[i];
if (rem == UWORD(0))
{
exp += (UWORD(1) << i);
(*n) = quot;
}
}
return exp;
}