mplogic.c

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/*
 *  mplogic.c
 *
 *  Bitwise logical operations on MPI values
 *
 * The contents of this file are subject to the Mozilla Public
 * License Version 1.1 (the "License"); you may not use this file
 * except in compliance with the License. You may obtain a copy of
 * the License at http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS
 * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * rights and limitations under the License.
 *
 * 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 Michael J. Fromberger are 
 * Copyright (C) 1998, 1999, 2000 Michael J. Fromberger. 
 * All Rights Reserved.
 *
 * Contributor(s):
 *
 * Alternatively, the contents of this file may be used under the
 * terms of the GNU General Public License Version 2 or later (the
 * "GPL"), in which case the provisions of the GPL are applicable
 * instead of those above.  If you wish to allow use of your
 * version of this file only under the terms of the GPL and not to
 * allow others to use your version of this file under the MPL,
 * indicate your decision by deleting the provisions above and
 * replace them with the notice and other provisions required by
 * the GPL.  If you do not delete the provisions above, a recipient
 * may use your version of this file under either the MPL or the GPL.
 *
 *  $Id: mplogic.c,v 1.12 2000/09/14 00:30:50 nelsonb%netscape.com Exp $
 */

#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_not(a, b)    - compute b = ~a
  mpl_and(a, b, c) - compute c = a & b
  mpl_or(a, b, c)  - compute c = a | b
  mpl_xor(a, b, c) - compute c = a ^ b
 */

/* {{{ mpl_not(a, b) */

mp_err mpl_not(mp_int *a, mp_int *b)
{
  mp_err   res;
  int      ix;

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

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

  /* This relies on the fact that the digit type is unsigned */
  for(ix = 0; ix < USED(b); ix++) 
    DIGIT(b, ix) = ~DIGIT(b, ix);

  s_mp_clamp(b);

  return MP_OKAY;

} /* end mpl_not() */

/* }}} */

/* {{{ mpl_and(a, b, c) */

mp_err mpl_and(mp_int *a, mp_int *b, mp_int *c)
{
  mp_int  *which, *other;
  mp_err   res;
  int      ix;

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

  if(USED(a) <= USED(b)) {
    which = a;
    other = b;
  } else {
    which = b;
    other = a;
  }

  if((res = mp_copy(which, c)) != MP_OKAY)
    return res;

  for(ix = 0; ix < USED(which); ix++)
    DIGIT(c, ix) &= DIGIT(other, ix);

  s_mp_clamp(c);

  return MP_OKAY;

} /* end mpl_and() */

/* }}} */

/* {{{ mpl_or(a, b, c) */

mp_err mpl_or(mp_int *a, mp_int *b, mp_int *c)
{
  mp_int  *which, *other;
  mp_err   res;
  int      ix;

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

  if(USED(a) >= USED(b)) {
    which = a;
    other = b;
  } else {
    which = b;
    other = a;
  }

  if((res = mp_copy(which, c)) != MP_OKAY)
    return res;

  for(ix = 0; ix < USED(which); ix++)
    DIGIT(c, ix) |= DIGIT(other, ix);

  return MP_OKAY;

} /* end mpl_or() */

/* }}} */

/* {{{ mpl_xor(a, b, c) */

mp_err mpl_xor(mp_int *a, mp_int *b, mp_int *c)
{
  mp_int  *which, *other;
  mp_err   res;
  int      ix;

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

  if(USED(a) >= USED(b)) {
    which = a;
    other = b;
  } else {
    which = b;
    other = a;
  }

  if((res = mp_copy(which, c)) != MP_OKAY)
    return res;

  for(ix = 0; ix < USED(which); ix++)
    DIGIT(c, ix) ^= DIGIT(other, ix);

  s_mp_clamp(c);

  return MP_OKAY;

} /* end mpl_xor() */

/* }}} */

/*------------------------------------------------------------------------*/
/*
  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_num_set(a, num)

  Count the number of set bits in the binary representation of a.
  Returns MP_OKAY and sets 'num' to be the number of such bits, if
  possible.  If num is NULL, the result is thrown away, but it is
  not considered an error.

  mpl_num_clear() does basically the same thing for clear bits.
 */

/* {{{ mpl_num_set(a, num) */

mp_err mpl_num_set(mp_int *a, int *num)
{
  int            ix, db, nset = 0;
  mp_digit       cur;
  unsigned char  reg;

  ARGCHK(a != NULL, MP_BADARG);

  for(ix = 0; ix < USED(a); ix++) {
    cur = DIGIT(a, ix);
    
    for(db = 0; db < sizeof(mp_digit); db++) {
      reg = (unsigned char)(cur >> (CHAR_BIT * db));

      nset += bitc[reg];
    }
  }

  if(num)
    *num = nset;

  return MP_OKAY;

} /* end mpl_num_set() */

/* }}} */

/* {{{ mpl_num_clear(a, num) */

mp_err mpl_num_clear(mp_int *a, int *num)
{
  int            ix, db, nset = 0;
  mp_digit       cur;
  unsigned char  reg;

  ARGCHK(a != NULL, MP_BADARG);

  for(ix = 0; ix < USED(a); ix++) {
    cur = DIGIT(a, ix);
    
    for(db = 0; db < sizeof(mp_digit); db++) {
      reg = (unsigned char)(cur >> (CHAR_BIT * db));

      nset += bitc[UCHAR_MAX - reg];
    }
  }

  if(num)
    *num = nset;

  return MP_OKAY;


} /* end mpl_num_clear() */

/* }}} */

/*------------------------------------------------------------------------*/
/*
  mpl_parity(a)

  Determines the bitwise parity of the value given.  Returns MP_EVEN
  if an even number of digits are set, MP_ODD if an odd number are
  set.
 */

/* {{{ mpl_parity(a) */

mp_err mpl_parity(mp_int *a)
{
  int      ix, par = 0;
  mp_digit cur;

  ARGCHK(a != NULL, MP_BADARG);

  for(ix = 0; ix < USED(a); ix++) {
    int   shft = (sizeof(mp_digit) * CHAR_BIT) / 2;

    cur = DIGIT(a, ix);

    /* Compute parity for current digit */
    while(shft != 0) {
      cur ^= (cur >> shft);
      shft >>= 1;
    }
    cur &= 1;

    /* XOR with running parity so far   */
    par ^= cur;
  }

  if(par)
    return MP_ODD;
  else
    return MP_EVEN;

} /* end mpl_parity() */

/* }}} */

/*
  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                                                  */