*

 *

 *

 *

 * The Original Code is the MPI Arbitrary Precision Integer Arithmetic library.

 *

 * The Initial Developer of the Original Code is

 * Michael J. Fromberger.

 * Portions created by the Initial Developer are Copyright (C) 1998

 * the Initial Developer. All Rights Reserved.

 *

 * Contributor(s):

 *

 *********************************************************************** */

#include "mpi-priv.h"

#include "mplogic.h"

/* {{{ Lookup table for population count */

static unsigned char bitc[] = {

   0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4,

   1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,

   1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,

   2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,

   1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,

   2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,

   2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,

   3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,

   1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,

   2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,

   2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,

   3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,

   2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,

   3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,

   3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,

   4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8

};

/* }}} */

/*

  mpl_rsh(a, b, d)     - b = a >> d

  mpl_lsh(a, b, d)     - b = a << d

 */

/* {{{ mpl_rsh(a, b, d) */

mp_err mpl_rsh(const mp_int *a, mp_int *b, mp_digit d)

{

  mp_err   res;

  ARGCHK(a != NULL && b != NULL, MP_BADARG);

  if((res = mp_copy(a, b)) != MP_OKAY)

    return res;

  s_mp_div_2d(b, d);

  return MP_OKAY;

} /* end mpl_rsh() */

/* }}} */

/* {{{ mpl_lsh(a, b, d) */

mp_err mpl_lsh(const mp_int *a, mp_int *b, mp_digit d)

{

  mp_err   res;

  ARGCHK(a != NULL && b != NULL, MP_BADARG);

  if((res = mp_copy(a, b)) != MP_OKAY)

    return res;

  return s_mp_mul_2d(b, d);

} /* end mpl_lsh() */

/* }}} */

/*------------------------------------------------------------------------*/

/*

  mpl_set_bit

  Returns MP_OKAY or some error code.

  Grows a if needed to set a bit to 1.

 */

mp_err mpl_set_bit(mp_int *a, mp_size bitNum, mp_size value)

{

  mp_size      ix;

  mp_err       rv;

  mp_digit     mask;

  ARGCHK(a != NULL, MP_BADARG);

  ix = bitNum / MP_DIGIT_BIT;

  if (ix + 1 > MP_USED(a)) {

    rv = s_mp_pad(a, ix + 1);

    if (rv != MP_OKAY)

      return rv;

  }

  bitNum = bitNum % MP_DIGIT_BIT;

  mask = (mp_digit)1 << bitNum;

  if (value)

    MP_DIGIT(a,ix) |= mask;

  else

    MP_DIGIT(a,ix) &= ~mask;

  s_mp_clamp(a);

  return MP_OKAY;

}

/*

  mpl_get_bit

  returns 0 or 1 or some (negative) error code.

 */

mp_err mpl_get_bit(const mp_int *a, mp_size bitNum)

{

  mp_size      bit, ix;

  mp_err       rv;

  ARGCHK(a != NULL, MP_BADARG);

  ix = bitNum / MP_DIGIT_BIT;

  ARGCHK(ix <= MP_USED(a) - 1, MP_RANGE);

  bit   = bitNum % MP_DIGIT_BIT;

  rv = (mp_err)(MP_DIGIT(a, ix) >> bit) & 1;

  return rv;

}

/*

  mpl_get_bits

  - Extracts numBits bits from a, where the least significant extracted bit

  is bit lsbNum.  Returns a negative value if error occurs.

  - Because sign bit is used to indicate error, maximum number of bits to

  be returned is the lesser of (a) the number of bits in an mp_digit, or

  (b) one less than the number of bits in an mp_err.

  - lsbNum + numbits can be greater than the number of significant bits in

  integer a, as long as bit lsbNum is in the high order digit of a.

 */

mp_err mpl_get_bits(const mp_int *a, mp_size lsbNum, mp_size numBits)

{

  mp_size    rshift = (lsbNum % MP_DIGIT_BIT);

  mp_size    lsWndx = (lsbNum / MP_DIGIT_BIT);

  mp_digit * digit  = MP_DIGITS(a) + lsWndx;

  mp_digit   mask   = ((1 << numBits) - 1);

  ARGCHK(numBits < CHAR_BIT * sizeof mask, MP_BADARG);

  ARGCHK(MP_HOWMANY(lsbNum, MP_DIGIT_BIT) <= MP_USED(a), MP_RANGE);

  if ((numBits + lsbNum % MP_DIGIT_BIT <= MP_DIGIT_BIT) ||

      (lsWndx + 1 >= MP_USED(a))) {

    mask &= (digit[0] >> rshift);

  } else {

    mask &= ((digit[0] >> rshift) | (digit[1] << (MP_DIGIT_BIT - rshift)));

  }

  return (mp_err)mask;

}

/*

  mpl_significant_bits

  returns number of significnant bits in abs(a).

  returns 1 if value is zero.

 */

mp_err mpl_significant_bits(const mp_int *a)

{

  mp_err bits   = 0;

  int    ix;

  ARGCHK(a != NULL, MP_BADARG);

  ix = MP_USED(a);

  for (ix = MP_USED(a); ix > 0; ) {

    mp_digit d;

    d = MP_DIGIT(a, --ix);

    if (d) {

      while (d) {

        ++bits;

        d >>= 1;

      }

      break;

    }

  }

  bits += ix * MP_DIGIT_BIT;

  if (!bits)

    bits = 1;

  return bits;

}

/*------------------------------------------------------------------------*/

/* HERE THERE BE DRAGONS                                                  */