sorted_stack_support.hpp

/* sdsl - succinct data structures library
    Copyright (C) 2009 Simon Gog

    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 3 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, see http://www.gnu.org/licenses/ .
*/
/*! \file sorted_stack_support.hpp
	\author Simon Gog
*/
#ifndef INCLUDED_SDSL_SORTED_STACK_SUPPORT
#define INCLUDED_SDSL_SORTED_STACK_SUPPORT

#include "int_vector.hpp"

namespace sdsl
{
//! A stack which contains strictly increasing numbers in the range from \f$0\f$ to \f$n\f$.
/*!
 *  \par Reference
 *  Johannes Fischer:
 *  Optimal Succinctness for Range Minimum Queries
 *  LATIN 2010
 *
 *  \par Space complexity
 *    \f$n\f$ bits
 */
class sorted_stack_support
{
    public:
        typedef int_vector<64>::size_type size_type;
    private:
        size_type m_n;   // Size of the supported vector.
        size_type m_cnt; // Counter for the indices on the stack.
        size_type m_top; // Topmost index of the stack.
        int_vector<64> m_stack; // Memory for the stack.

        inline size_type block_nr(size_type x) {
            return x/63;
        }; // TODO: maybe we can speed this up with bit hacks
        inline size_type block_pos(size_type x) {
            return x%63;
        }; // TODO: maybe we can speed this up with bit hacks
    public:
        //! Constructor
        /*! \param n Maximum that can be pushed onto the stack
         */
        sorted_stack_support(size_type n);

        sorted_stack_support(const sorted_stack_support&) = default;
        sorted_stack_support(sorted_stack_support&&) = default;
        sorted_stack_support& operator=(const sorted_stack_support&) = default;
        sorted_stack_support& operator=(sorted_stack_support&&) = default;

        /*! Returns if the stack is empty.
         */
        bool empty() const {
            return 0==m_cnt;
        };

        /*! Returns the topmost index on the stack.
         * \pre empty()==false
         */
        size_type top() const;

        /*! Pop the topmost index of the stack.
         */
        void pop();

        /*! Push the index x of vector vec onto the stack.
         * \par x Index of the value in vec which should be pushed onto the stack.
         * \pre top() < x and x <= n
         */
        void push(size_type x);

        /*! Returns the number of element is the stack.
         */
        size_type size()const {
            return m_cnt;
        };

        size_type
        serialize(std::ostream& out, structure_tree_node* v=nullptr,
                  std::string name="")const;
        void load(std::istream& in);

};

inline sorted_stack_support::sorted_stack_support(size_type n):m_n(n), m_cnt(0), m_top(0), m_stack()
{
    m_stack = int_vector<64>(block_nr(m_n+1)+1, 0);
    m_stack[0] = 1;
}

inline sorted_stack_support::size_type sorted_stack_support::top()const
{
    assert(empty() == false);
    return m_top-1;
}

inline void sorted_stack_support::push(size_type x)
{
    assert((empty() or top() < x) and x <= m_n);
    x += 1;
    ++m_cnt;	//< increment counter
    size_type bn = block_nr(x);
    m_stack[bn] ^= (1ULL << block_pos(x));
    if (bn > 0 and m_stack[bn-1] == 0) {
        m_stack[bn-1] = 0x8000000000000000ULL | m_top;
    }
    m_top = x;
}

inline void sorted_stack_support::pop()
{
    if (!empty()) {
        --m_cnt; //< decrement counter
        size_type bn = block_nr(m_top);
        uint64_t w = m_stack[ bn ];
        assert((w>>63) == 0);    // highest bit is not set, as the block contains no pointer
        w ^= (1ULL << block_pos(m_top));
        m_stack[ bn ] = w;
        if (w>0) {
            m_top = bn*63 + bits::hi(w);
        } else { // w==0 and cnt>0
            assert(bn > 0);
            w = m_stack[ bn-1 ];
            if ((w>>63) == 0) { // highest bit is not set => the block contains no pointer
                assert(w>0);
                m_top = (bn-1)*63 + bits::hi(w);
            } else { // block contains pointers
                m_stack[bn-1] = 0;
                m_top = w&0x7FFFFFFFFFFFFFFFULL;
            }
        }
    }
}

inline sorted_stack_support::size_type
sorted_stack_support::serialize(std::ostream& out, structure_tree_node* v,
                                std::string name)const
{
    structure_tree_node* child = structure_tree::add_child(v, name, util::class_name(*this));
    size_type written_bytes = 0;
    written_bytes += write_member(m_n, out);
    written_bytes += write_member(m_top, out);
    written_bytes += write_member(m_cnt, out);
    written_bytes += m_stack.serialize(out);
    structure_tree::add_size(child, written_bytes);
    return written_bytes;
}

inline void sorted_stack_support::load(std::istream& in)
{
    read_member(m_n, in);
    read_member(m_top, in);
    read_member(m_cnt, in);
    m_stack.load(in);
}

}// end namespace sdsl

#endif // end file