pqc/external/flint-2.4.3/ulong_extras/powmod2_preinv.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"
mp_limb_t
n_powmod2_ui_preinv(mp_limb_t a, mp_limb_t exp, mp_limb_t n, mp_limb_t ninv)
{
mp_limb_t x, y;
if (n == UWORD(1)) return UWORD(0);
x = UWORD(1);
y = a;
while (exp)
{
if (exp & 1) x = n_mulmod2_preinv(x, y, n, ninv);
exp >>= 1;
if (exp) y = n_mulmod2_preinv(y, y, n, ninv);
}
return x;
}
mp_limb_t
n_powmod2_preinv(mp_limb_t a, mp_limb_signed_t exp, mp_limb_t n, mp_limb_t ninv)
{
if (exp < WORD(0))
{
a = n_invmod(a, n);
exp = -exp;
}
return n_powmod2_ui_preinv(a, exp, n, ninv);
}