/* ecc-mul-a-eh.c

   Copyright (C) 2013, 2014 Niels Möller

   This file is part of GNU Nettle.

   GNU Nettle is free software: you can redistribute it and/or

   modify it under the terms of either:

     * the GNU Lesser General Public License as published by the Free

       Software Foundation; either version 3 of the License, or (at your

       option) any later version.

   or

     * 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.

   or both in parallel, as here.

   GNU Nettle 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 copies of the GNU General Public License and

   the GNU Lesser General Public License along with this program.  If

   not, see http://www.gnu.org/licenses/.

*/

#if HAVE_CONFIG_H

# include "config.h"

#endif

#include <assert.h>

#include "ecc.h"

#include "ecc-internal.h"

/* Binary algorithm needs 6*ecc->p.size + scratch for ecc_add_ehh,

   total 10 ecc->p.size

   Window algorithm needs (3<<w) * ecc->p.size for the table,

   3*ecc->p.size for a temporary point, and scratch for

   ecc_add_ehh. */

#if ECC_MUL_A_EH_WBITS == 0

void

ecc_mul_a_eh (const struct ecc_curve *ecc,

        mp_limb_t *r,

        const mp_limb_t *np, const mp_limb_t *p,

        mp_limb_t *scratch)

{

#define pe scratch

#define tp (scratch + 3*ecc->p.size)

#define scratch_out (scratch + 6*ecc->p.size)

  unsigned i;

  ecc_a_to_j (ecc, pe, p);

  /* x = 0, y = 1, z = 1 */

  mpn_zero (r, 3*ecc->p.size);

  r[ecc->p.size] = r[2*ecc->p.size] = 1;

  for (i = ecc->p.size; i-- > 0; )

    {

      mp_limb_t w = np[i];

      mp_limb_t bit;

      for (bit = (mp_limb_t) 1 << (GMP_NUMB_BITS - 1);

     bit > 0;

     bit >>= 1)

  {

    int digit;

    ecc->dup (ecc, r, r, scratch_out);

    ecc->add_hh (ecc, tp, r, pe, scratch_out);

    digit = (w & bit) > 0;

    /* If we had a one-bit, use the sum. */

    cnd_copy (digit, r, tp, 3*ecc->p.size);

  }

    }

}

#else /* ECC_MUL_A_EH_WBITS > 1 */

#define TABLE_SIZE (1U << ECC_MUL_A_EH_WBITS)

#define TABLE_MASK (TABLE_SIZE - 1)

#define TABLE(j) (table + (j) * 3*ecc->p.size)

static void

table_init (const struct ecc_curve *ecc,

      mp_limb_t *table, unsigned bits,

      const mp_limb_t *p,

      mp_limb_t *scratch)

{

  unsigned size = 1 << bits;

  unsigned j;

  mpn_zero (TABLE(0), 3*ecc->p.size);

  TABLE(0)[ecc->p.size] = TABLE(0)[2*ecc->p.size] = 1;

  ecc_a_to_j (ecc, TABLE(1), p);

  for (j = 2; j < size; j += 2)

    {

      ecc->dup (ecc, TABLE(j), TABLE(j/2), scratch);

      ecc->add_hh (ecc, TABLE(j+1), TABLE(j), TABLE(1), scratch);

    }

}

void

ecc_mul_a_eh (const struct ecc_curve *ecc,

        mp_limb_t *r,

        const mp_limb_t *np, const mp_limb_t *p,

        mp_limb_t *scratch)

{

#define tp scratch

#define table (scratch + 3*ecc->p.size)

  mp_limb_t *scratch_out = table + (3*ecc->p.size << ECC_MUL_A_EH_WBITS);

  /* Avoid the mp_bitcnt_t type for compatibility with older GMP

     versions. */

  unsigned blocks = (ecc->p.bit_size + ECC_MUL_A_EH_WBITS - 1) / ECC_MUL_A_EH_WBITS;

  unsigned bit_index = (blocks-1) * ECC_MUL_A_EH_WBITS;

  mp_size_t limb_index = bit_index / GMP_NUMB_BITS;

  unsigned shift = bit_index % GMP_NUMB_BITS;

  mp_limb_t w, bits;

  table_init (ecc, table, ECC_MUL_A_EH_WBITS, p, scratch_out);

  w = np[limb_index];

  bits = w >> shift;

  if (limb_index < ecc->p.size - 1)

    bits |= np[limb_index + 1] << (GMP_NUMB_BITS - shift);

  assert (bits < TABLE_SIZE);

  mpn_sec_tabselect (r, table, 3*ecc->p.size, TABLE_SIZE, bits);

  for (;;)

    {

      unsigned j;

      if (shift >= ECC_MUL_A_EH_WBITS)

  {

    shift -= ECC_MUL_A_EH_WBITS;

    bits = w >> shift;

  }

      else

  {

    if (limb_index == 0)

      {

        assert (shift == 0);

        break;

      }

    bits = w << (ECC_MUL_A_EH_WBITS - shift);

    w = np[--limb_index];

    shift = shift + GMP_NUMB_BITS - ECC_MUL_A_EH_WBITS;

    bits |= w >> shift;

  }

      for (j = 0; j < ECC_MUL_A_EH_WBITS; j++)

  ecc->dup (ecc, r, r, scratch_out);

      bits &= TABLE_MASK;

      mpn_sec_tabselect (tp, table, 3*ecc->p.size, TABLE_SIZE, bits);

      ecc->add_hhh (ecc, r, r, tp, scratch_out);

    }

#undef table

#undef tp

}

#endif /* ECC_MUL_A_EH_WBITS > 1 */