aria2/src/bitfield.h

/* <!-- copyright */
/*
 * aria2 - The high speed download utility
 *
 * Copyright (C) 2009 Tatsuhiro Tsujikawa
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of 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.
 *
 * This program 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 a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 *
 * In addition, as a special exception, the copyright holders give
 * permission to link the code of portions of this program with the
 * OpenSSL library under certain conditions as described in each
 * individual source file, and distribute linked combinations
 * including the two.
 * You must obey the GNU General Public License in all respects
 * for all of the code used other than OpenSSL.  If you modify
 * file(s) with this exception, you may extend this exception to your
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 * do not wish to do so, delete this exception statement from your
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 */
/* copyright --> */
#ifndef D_BITFIELD_H
#define D_BITFIELD_H

#include "common.h"

#include <cassert>
#include <cstdlib>
#include <cstring>

#include "util.h"

namespace aria2 {

namespace bitfield {

// Returns the bit mask for the last byte. For example, nbits = 9,
// then 0x80u is returned. nbits = 12, then 0xf0u is returned.
inline unsigned char lastByteMask(size_t nbits)
{
  if (nbits == 0) {
    return 0;
  }
  else {
    int s = nbits % 8;
    if (s == 0) {
      return 0xffu;
    }
    else {
      return -256 >> s;
    }
  }
}

// Returns true if index-th bits is set. Otherwise returns false.
template <typename Array>
inline bool test(const Array& bitfield, size_t nbits, size_t index)
{
  assert(index < nbits);
  unsigned char mask = 128 >> (index % 8);
  return (bitfield[index / 8] & mask) != 0;
}

const int cntbits[] = {
    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,
};

inline size_t countBit32(uint32_t n)
{
  return cntbits[n & 0xffu] + cntbits[(n >> 8) & 0xffu] +
         cntbits[(n >> 16) & 0xffu] + cntbits[(n >> 24) & 0xffu];
}

// Counts set bit in bitfield.
inline size_t countSetBit(const unsigned char* bitfield, size_t nbits)
{
  if (nbits == 0) {
    return 0;
  }
  size_t count = 0;
  size_t size = sizeof(uint32_t);
  size_t len = (nbits + 7) / 8;
  if (nbits % 32 != 0) {
    --len;
    count +=
        countBit32(static_cast<uint32_t>(bitfield[len] & lastByteMask(nbits)));
  }
  size_t to = len / size;
  for (size_t i = 0; i < to; ++i) {
    uint32_t v;
    memcpy(&v, &bitfield[i * size], sizeof(v));
    count += countBit32(v);
  }
  for (size_t i = len - len % size; i < len; ++i) {
    count += countBit32(static_cast<uint32_t>(bitfield[i]));
  }
  return count;
}

// Counts set bit in bitfield. This is a bit slower than countSetBit
// but can accept array template expression as bitfield.
template <typename Array>
size_t countSetBitSlow(const Array& bitfield, size_t nbits)
{
  if (nbits == 0) {
    return 0;
  }
  size_t count = 0;
  size_t to = (nbits + 7) / 8;
  if (to > 1) {
    for (size_t i = 0; i < to - 1; ++i) {
      count += cntbits[static_cast<unsigned char>(bitfield[i])];
    }
  }
  count += cntbits[static_cast<unsigned char>(bitfield[to - 1]) &
                   lastByteMask(nbits)];
  return count;
}

void flipBit(unsigned char* data, size_t length, size_t bitIndex);

// Stores first set bit index of bitfield to index.  bitfield contains
// nbits. Returns true if set bit is found. Otherwise returns false.
template <typename Array>
bool getFirstSetBitIndex(size_t& index, const Array& bitfield, size_t nbits)
{
  for (size_t i = 0; i < nbits; ++i) {
    if (bitfield::test(bitfield, nbits, i)) {
      index = i;
      return true;
    }
  }
  return false;
}

// Appends first at most n set bit index in bitfield to out.  bitfield
// contains nbits bits.  Returns the number of appended bit indexes.
template <typename Array, typename OutputIterator>
size_t getFirstNSetBitIndex(OutputIterator out, size_t n, const Array& bitfield,
                            size_t nbits)
{
  if (n == 0) {
    return 0;
  }
  const size_t origN = n;
  for (size_t i = 0; i < nbits; ++i) {
    if (bitfield::test(bitfield, nbits, i)) {
      *out++ = i;
      if (--n == 0) {
        break;
      }
    }
  }
  return origN - n;
}

} // namespace bitfield

} // namespace aria2

#endif // D_BITFIELD_H