/*

 *  mplogic.c

 *

 *  Bitwise logical operations on MPI values

 *

 * This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#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;

    unsigned 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;

    unsigned 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;

    unsigned 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;

    unsigned 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, unsigned int *num)

{

    unsigned 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, unsigned int *num)

{

    unsigned 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)

{

    unsigned int ix;

    int 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;

}

#define LZCNTLOOP(i)                               \

    do {                                           \

        x = d >> (i);                              \

        mask = (0 - x);                            \

        mask = (0 - (mask >> (MP_DIGIT_BIT - 1))); \

        bits += (i)&mask;                          \

        d ^= (x ^ d) & mask;                       \

    } while (0)

/*

  mpl_significant_bits

  returns number of significant bits in abs(a).

  In other words: floor(lg(abs(a))) + 1.

  returns 1 if value is zero.

 */

mp_size

mpl_significant_bits(const mp_int *a)

{

    /*

      start bits at 1.

      lg(0) = 0 => bits = 1 by function semantics.

      below does a binary search for the _position_ of the top bit set,

      which is floor(lg(abs(a))) for a != 0.

     */

    mp_size bits = 1;

    int ix;

    ARGCHK(a != NULL, MP_BADARG);

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

        mp_digit d, x, mask;

        if ((d = MP_DIGIT(a, --ix)) == 0)

            continue;

#if !defined(MP_USE_UINT_DIGIT)

        LZCNTLOOP(32);

#endif

        LZCNTLOOP(16);

        LZCNTLOOP(8);

        LZCNTLOOP(4);

        LZCNTLOOP(2);

        LZCNTLOOP(1);

        break;

    }

    bits += ix * MP_DIGIT_BIT;

    return bits;

}

#undef LZCNTLOOP

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

/* HERE THERE BE DRAGONS                                                  */