path: root/security/nss/lib/freebl/mpi/mplogic.c

/*
 *  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, int *num)
{
    unsigned int ix;
    int 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)
{
    unsigned int ix;
    int 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                                                  */