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/* sec-tabselect.c */
/* nettle, low-level cryptographics library
*
* Copyright (C) 2013 Niels Möller
*
* The nettle library is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2.1 of the License, or (at your
* option) any later version.
*
* The nettle library 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 Lesser General Public
* License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with the nettle library; see the file COPYING.LIB. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
* MA 02111-1301, USA.
*/
/* Development of Nettle's ECC support was funded by the .SE Internet Fund. */
#if HAVE_CONFIG_H
# include "config.h"
#endif
#include <assert.h>
#include "ecc-internal.h"
/* Copy the k'th element of the table out tn elements, each of size
rn. Always read complete table. Similar to gmp's mpn_tabselect. */
/* FIXME: Should we need to volatile declare anything? */
void
sec_tabselect (mp_limb_t *rp, mp_size_t rn,
const mp_limb_t *table, unsigned tn,
unsigned k)
{
const mp_limb_t *end = table + tn * rn;
const mp_limb_t *p;
mp_size_t i;
assert (k < tn);
mpn_zero (rp, rn);
for (p = table; p < end; p += rn, k--)
{
mp_limb_t mask = - (mp_limb_t) (k == 0);
for (i = 0; i < rn; i++)
rp[i] += mask & p[i];
}
}
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