smul_precomp.c

/* Copyright 2008-2019 Douglas Wikstrom
 *
 * This file is part of Verificatum Elliptic Curve library (VEC).
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use, copy,
 * modify, merge, publish, distribute, sublicense, and/or sell copies
 * of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#include <stdio.h>
#include <gmp.h>
#include "vec.h"

void
vec_smul_precomp(vec_smul_tab table, mpz_t *basesx, mpz_t *basesy)
{
  size_t i, j;        /* Index variables. */
  size_t block_width; /* Width of current subtable. */
  mpz_t *tx;          /* Temporary variable for subtable. */
  mpz_t *ty;          /* Temporary variable for subtable. */

  vec_scratch_mpz_t scratch;

  int mask;           /* Mask used for dynamic programming */
  int one_mask;       /* Mask containing a single non-zero bit. */

  vec_scratch_init_mpz_t(scratch);

  block_width = table->block_width;

  for (i = 0; i < table->tabs_len; i++)
    {
      /* Last block may have smaller width, but the width is never
         zero. */
      if (i == table->tabs_len - 1)
        {
          block_width = table->len - (table->tabs_len - 1) * block_width;
        }

      /* Current subtable. */
      tx = table->tabsx[i];
      ty = table->tabsy[i];

      /* Initialize current subtable with all trivial products. */
      mpz_set_si(tx[0], -1);
      mpz_set_si(ty[0], -1);

      mask = 1;
      for (j = 0; j < block_width; j++)
        {
          mpz_set(tx[mask], basesx[j]);
          mpz_set(ty[mask], basesy[j]);
          mask <<= 1;
        }

      /* Initialize current subtable with all non-trivial products. */
      for (mask = 1; mask < (1 << block_width); mask++)
        {
          one_mask = mask & (-mask);

          vec_add(scratch,
                  tx[mask], ty[mask],
                  table->curve,
                  tx[mask ^ one_mask], ty[mask ^ one_mask],
                  tx[one_mask], ty[one_mask]);
        }

      basesx += block_width;
      basesy += block_width;
    }

  vec_scratch_clear_mpz_t(scratch);
}