/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * vim: set ts=8 sts=4 et sw=4 tw=99:
 * 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/. */

#ifndef ds_BitArray_h
#define ds_BitArray_h

#include "mozilla/TemplateLib.h"

#include <limits.h>
#include <string.h>

#include "jstypes.h"

namespace js {

template <size_t nbits>
class BitArray
{
  private:
    // Use a 32 bit word to make it easier to access a BitArray from JIT code.
    using WordT = uint32_t;

    static const size_t bitsPerElement = sizeof(WordT) * CHAR_BIT;
    static const size_t numSlots = nbits / bitsPerElement + (nbits % bitsPerElement == 0 ? 0 : 1);
    static const size_t paddingBits = (numSlots * bitsPerElement) - nbits;
    static_assert(paddingBits < bitsPerElement, "More padding bits than expected.");
    static const WordT paddingMask = WordT(-1) >> paddingBits;

    WordT map[numSlots];

  public:
    constexpr BitArray() : map() {};

    void clear(bool value) {
        memset(map, value ? 0xFF : 0, sizeof(map));
        if (value) {
            map[numSlots - 1] &= paddingMask;
        }
    }

    inline bool get(size_t offset) const {
        size_t index;
        WordT mask;
        getIndexAndMask(offset, &index, &mask);
        return map[index] & mask;
    }

    void set(size_t offset) {
        size_t index;
        WordT mask;
        getIndexAndMask(offset, &index, &mask);
        map[index] |= mask;
    }

    void unset(size_t offset) {
        size_t index;
        WordT mask;
        getIndexAndMask(offset, &index, &mask);
        map[index] &= ~mask;
    }

    bool isAllClear() const {
        for (size_t i = 0; i < numSlots; i++) {
            if (map[i]) {
                return false;
            }
        }
        return true;
    }

    static void getIndexAndMask(size_t offset, size_t* indexp, WordT* maskp) {
        static_assert(bitsPerElement == 32, "unexpected bitsPerElement value");
        *indexp = offset / bitsPerElement;
        *maskp = WordT(1) << (offset % bitsPerElement);
    }

    static size_t offsetOfMap() {
        return offsetof(BitArray<nbits>, map);
    }
};

} /* namespace js */

#endif /* ds_BitArray_h */
