// Copyright (c) 2018 Google LLC

//

// Licensed under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0

//

// Unless required by applicable law or agreed to in writing, software

// distributed under the License is distributed on an "AS IS" BASIS,

// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

// See the License for the specific language governing permissions and

// limitations under the License.

#ifndef SOURCE_UTIL_BIT_VECTOR_H_

#define SOURCE_UTIL_BIT_VECTOR_H_

#include <cstdint>

#include <iosfwd>

#include <vector>

namespace spvtools {

namespace utils {

// Implements a bit vector class.

//

// All bits default to zero, and the upper bound is 2^32-1.

class BitVector {

 private:

  using BitContainer = uint64_t;

  enum { kBitContainerSize = 64 };

  enum { kInitialNumBits = 1024 };

 public:

  // Creates a bit vector containing 0s.

  BitVector(uint32_t reserved_size = kInitialNumBits)

      : bits_((reserved_size - 1) / kBitContainerSize + 1, 0) {}

  // Sets the |i|th bit to 1.  Returns the |i|th bit before it was set.

  bool Set(uint32_t i) {

    uint32_t element_index = i / kBitContainerSize;

    uint32_t bit_in_element = i % kBitContainerSize;

    if (element_index >= bits_.size()) {

      bits_.resize(element_index + 1, 0);

    }

    BitContainer original = bits_[element_index];

    BitContainer ith_bit = static_cast<BitContainer>(1) << bit_in_element;

    if ((original & ith_bit) != 0) {

      return true;

    } else {

      bits_[element_index] = original | ith_bit;

      return false;

    }

  }

  // Sets the |i|th bit to 0.  Return the |i|th bit before it was cleared.

  bool Clear(uint32_t i) {

    uint32_t element_index = i / kBitContainerSize;

    uint32_t bit_in_element = i % kBitContainerSize;

    if (element_index >= bits_.size()) {

      return false;

    }

    BitContainer original = bits_[element_index];

    BitContainer ith_bit = static_cast<BitContainer>(1) << bit_in_element;

    if ((original & ith_bit) == 0) {

      return false;

    } else {

      bits_[element_index] = original & (~ith_bit);

      return true;

    }

  }

  // Returns the |i|th bit.

  bool Get(uint32_t i) const {

    uint32_t element_index = i / kBitContainerSize;

    uint32_t bit_in_element = i % kBitContainerSize;

    if (element_index >= bits_.size()) {

      return false;

    }

    return (bits_[element_index] &

            (static_cast<BitContainer>(1) << bit_in_element)) != 0;

  }

  // Returns true if every bit is 0.

  bool Empty() const {

    for (BitContainer b : bits_) {

      if (b != 0) {

        return false;

      }

    }

    return true;

  }

  // Print a report on the densicy of the bit vector, number of 1 bits, number

  // of bytes, and average bytes for 1 bit, to |out|.

  void ReportDensity(std::ostream& out);

  friend std::ostream& operator<<(std::ostream&, const BitVector&);

  // Performs a bitwise-or operation on |this| and |that|, storing the result in

  // |this|.  Return true if |this| changed.

  bool Or(const BitVector& that);

 private:

  std::vector<BitContainer> bits_;

};

}  // namespace utils

}  // namespace spvtools

#endif  // SOURCE_UTIL_BIT_VECTOR_H_