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/* ecc-mul-g.c
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Copyright (C) 2013 Niels Möller
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This file is part of GNU Nettle.
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GNU Nettle is free software: you can redistribute it and/or
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modify it under the terms of either:
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* the GNU Lesser General Public License as published by the Free
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Software Foundation; either version 3 of the License, or (at your
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option) any later version.
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or
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* the GNU General Public License as published by the Free
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Software Foundation; either version 2 of the License, or (at your
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option) any later version.
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or both in parallel, as here.
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GNU Nettle is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received copies of the GNU General Public License and
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the GNU Lesser General Public License along with this program. If
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not, see http://www.gnu.org/licenses/.
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*/
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/* Development of Nettle's ECC support was funded by the .SE Internet Fund. */
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#if HAVE_CONFIG_H
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# include "config.h"
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#endif
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#include <nettle/ecc.h>
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#include "ecc-internal.h"
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void
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ecc_mul_g (const struct ecc_curve *ecc, mp_limb_t *r,
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const mp_limb_t *np, mp_limb_t *scratch)
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{
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/* Scratch need determined by the ecc_add_jja call. Current total is
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9 * ecc->p.size, at most 648 bytes. */
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#define tp scratch
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#define scratch_out (scratch + 3*ecc->p.size)
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unsigned k, c;
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unsigned i, j;
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unsigned bit_rows;
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int is_zero;
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k = ecc->pippenger_k;
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c = ecc->pippenger_c;
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bit_rows = (ecc->p.bit_size + k - 1) / k;
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mpn_zero (r, 3*ecc->p.size);
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for (i = k, is_zero = 1; i-- > 0; )
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{
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ecc_dup_jj (ecc, r, r, scratch);
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for (j = 0; j * c < bit_rows; j++)
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{
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unsigned bits;
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/* Avoid the mp_bitcnt_t type for compatibility with older GMP
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versions. */
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unsigned bit_index;
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/* Extract c bits from n, stride k, starting at i + kcj,
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ending at i + k (cj + c - 1)*/
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for (bits = 0, bit_index = i + k*(c*j+c); bit_index > i + k*c*j; )
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{
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mp_size_t limb_index;
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unsigned shift;
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bit_index -= k;
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limb_index = bit_index / GMP_NUMB_BITS;
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if (limb_index >= ecc->p.size)
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continue;
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shift = bit_index % GMP_NUMB_BITS;
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bits = (bits << 1) | ((np[limb_index] >> shift) & 1);
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}
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sec_tabselect (tp, 2*ecc->p.size,
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(ecc->pippenger_table
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+ (2*ecc->p.size * (mp_size_t) j << c)),
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1<
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cnd_copy (is_zero, r, tp, 2*ecc->p.size);
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cnd_copy (is_zero, r + 2*ecc->p.size, ecc->unit, ecc->p.size);
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ecc_add_jja (ecc, tp, r, tp, scratch_out);
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/* Use the sum when valid. ecc_add_jja produced garbage if
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is_zero != 0 or bits == 0, . */
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cnd_copy (bits & (is_zero - 1), r, tp, 3*ecc->p.size);
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is_zero &= (bits == 0);
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}
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}
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#undef tp
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#undef scratch_out
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}
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