trie.cpp

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/*
    Copyright (c) 2007-2016 Contributors as noted in the AUTHORS file

    This file is part of libzmq, the ZeroMQ core engine in C++.

    libzmq is free software; you can redistribute it and/or modify it under
    the terms of the GNU Lesser General Public License (LGPL) as published
    by the Free Software Foundation; either version 3 of the License, or
    (at your option) any later version.

    As a special exception, the Contributors give you permission to link
    this library with independent modules to produce an executable,
    regardless of the license terms of these independent modules, and to
    copy and distribute the resulting executable under terms of your choice,
    provided that you also meet, for each linked independent module, the
    terms and conditions of the license of that module. An independent
    module is a module which is not derived from or based on this library.
    If you modify this library, you must extend this exception to your
    version of the library.

    libzmq 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 Lesser General Public
    License for more details.

    You should have received a copy of the GNU Lesser General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "precompiled.hpp"
#include <stdlib.h>

#include <new>
#include <algorithm>

#include "macros.hpp"
#include "platform.hpp"
#if defined ZMQ_HAVE_WINDOWS
#include "windows.hpp"
#endif

#include "err.hpp"
#include "trie.hpp"

zmq::trie_t::trie_t () :
    refcnt (0),
    min (0),
    count (0),
    live_nodes (0)
{
}

zmq::trie_t::~trie_t ()
{
    if (count == 1) {
        zmq_assert (next.node);
        LIBZMQ_DELETE(next.node);
    }
    else if (count > 1) {
        for (unsigned short i = 0; i != count; ++i) {
            LIBZMQ_DELETE(next.table[i]);
        }
        free (next.table);
    }
}

bool zmq::trie_t::add (unsigned char *prefix_, size_t size_)
{
    //  We are at the node corresponding to the prefix. We are done.
    if (!size_) {
        ++refcnt;
        return refcnt == 1;
    }

    unsigned char c = *prefix_;
    if (c < min || c >= min + count) {

        //  The character is out of range of currently handled
        //  characters. We have to extend the table.
        if (!count) {
            min = c;
            count = 1;
            next.node = NULL;
        }
        else
        if (count == 1) {
            unsigned char oldc = min;
            trie_t *oldp = next.node;
            count = (min < c ? c - min : min - c) + 1;
            next.table = (trie_t**)
                malloc (sizeof (trie_t*) * count);
            alloc_assert (next.table);
            for (unsigned short i = 0; i != count; ++i)
                next.table [i] = 0;
            min = std::min (min, c);
            next.table [oldc - min] = oldp;
        }
        else
        if (min < c) {
            //  The new character is above the current character range.
            unsigned short old_count = count;
            count = c - min + 1;
            next.table = (trie_t**) realloc ((void*) next.table,
                sizeof (trie_t*) * count);
            zmq_assert (next.table);
            for (unsigned short i = old_count; i != count; i++)
                next.table [i] = NULL;
        }
        else {

            //  The new character is below the current character range.
            unsigned short old_count = count;
            count = (min + old_count) - c;
            next.table = (trie_t**) realloc ((void*) next.table,
                sizeof (trie_t*) * count);
            zmq_assert (next.table);
            memmove (next.table + min - c, next.table,
                old_count * sizeof (trie_t*));
            for (unsigned short i = 0; i != min - c; i++)
                next.table [i] = NULL;
            min = c;
        }
    }

    //  If next node does not exist, create one.
    if (count == 1) {
        if (!next.node) {
            next.node = new (std::nothrow) trie_t;
            alloc_assert (next.node);
            ++live_nodes;
            zmq_assert (live_nodes == 1);
        }
        return next.node->add (prefix_ + 1, size_ - 1);
    }
    else {
        if (!next.table [c - min]) {
            next.table [c - min] = new (std::nothrow) trie_t;
            alloc_assert (next.table [c - min]);
            ++live_nodes;
            zmq_assert (live_nodes > 1);
        }
        return next.table [c - min]->add (prefix_ + 1, size_ - 1);
    }
}

bool zmq::trie_t::rm (unsigned char *prefix_, size_t size_)
{
    //  TODO: Shouldn't an error be reported if the key does not exist?
    if (!size_) {
        if (!refcnt)
            return false;
        refcnt--;
        return refcnt == 0;
    }
    unsigned char c = *prefix_;
    if (!count || c < min || c >= min + count)
        return false;

    trie_t *next_node =
        count == 1 ? next.node : next.table [c - min];

    if (!next_node)
        return false;

    bool ret = next_node->rm (prefix_ + 1, size_ - 1);

    //  Prune redundant nodes
    if (next_node->is_redundant ()) {
        LIBZMQ_DELETE(next_node);
        zmq_assert (count > 0);

        if (count == 1) {
            //  The just pruned node is was the only live node
            next.node = 0;
            count = 0;
            --live_nodes;
            zmq_assert (live_nodes == 0);
        }
        else {
            next.table [c - min] = 0;
            zmq_assert (live_nodes > 1);
            --live_nodes;

            //  Compact the table if possible
            if (live_nodes == 1) {
                //  We can switch to using the more compact single-node
                //  representation since the table only contains one live node
                trie_t *node = 0;
                //  Since we always compact the table the pruned node must
                //  either be the left-most or right-most ptr in the node
                //  table
                if (c == min) {
                    //  The pruned node is the left-most node ptr in the
                    //  node table => keep the right-most node
                    node = next.table [count - 1];
                    min += count - 1;
                }
                else
                if (c == min + count - 1) {
                    //  The pruned node is the right-most node ptr in the
                    //  node table => keep the left-most node
                    node = next.table [0];
                }
                zmq_assert (node);
                free (next.table);
                next.node = node;
                count = 1;
            }
            else
            if (c == min) {
                //  We can compact the table "from the left".
                //  Find the left-most non-null node ptr, which we'll use as
                //  our new min
                unsigned char new_min = min;
                for (unsigned short i = 1; i < count; ++i) {
                    if (next.table [i]) {
                        new_min = i + min;
                        break;
                    }
                }
                zmq_assert (new_min != min);

                trie_t **old_table = next.table;
                zmq_assert (new_min > min);
                zmq_assert (count > new_min - min);

                count = count - (new_min - min);
                next.table = (trie_t**) malloc (sizeof (trie_t*) * count);
                alloc_assert (next.table);

                memmove (next.table, old_table + (new_min - min),
                        sizeof (trie_t*) * count);
                free (old_table);

                min = new_min;
            }
            else
            if (c == min + count - 1) {
                //  We can compact the table "from the right".
                //  Find the right-most non-null node ptr, which we'll use to
                //  determine the new table size
                unsigned short new_count = count;
                for (unsigned short i = 1; i < count; ++i) {
                    if (next.table [count - 1 - i]) {
                        new_count = count - i;
                        break;
                    }
                }
                zmq_assert (new_count != count);
                count = new_count;

                trie_t **old_table = next.table;
                next.table = (trie_t**) malloc (sizeof (trie_t*) * count);
                alloc_assert (next.table);

                memmove (next.table, old_table, sizeof (trie_t*) * count);
                free (old_table);
            }
        }
    }
    return ret;
}

bool zmq::trie_t::check (unsigned char *data_, size_t size_)
{
    //  This function is on critical path. It deliberately doesn't use
    //  recursion to get a bit better performance.
    trie_t *current = this;
    while (true) {

        //  We've found a corresponding subscription!
        if (current->refcnt)
            return true;

        //  We've checked all the data and haven't found matching subscription.
        if (!size_)
            return false;

        //  If there's no corresponding slot for the first character
        //  of the prefix, the message does not match.
        unsigned char c = *data_;
        if (c < current->min || c >= current->min + current->count)
            return false;

        //  Move to the next character.
        if (current->count == 1)
            current = current->next.node;
        else {
            current = current->next.table [c - current->min];
            if (!current)
                return false;
        }
        data_++;
        size_--;
    }
}

void zmq::trie_t::apply (void (*func_) (unsigned char *data_, size_t size_,
    void *arg_), void *arg_)
{
    unsigned char *buff = NULL;
    apply_helper (&buff, 0, 0, func_, arg_);
    free (buff);
}

void zmq::trie_t::apply_helper (
    unsigned char **buff_, size_t buffsize_, size_t maxbuffsize_,
    void (*func_) (unsigned char *data_, size_t size_, void *arg_), void *arg_)
{
    //  If this node is a subscription, apply the function.
    if (refcnt)
        func_ (*buff_, buffsize_, arg_);

    //  Adjust the buffer.
    if (buffsize_ >= maxbuffsize_) {
        maxbuffsize_ = buffsize_ + 256;
        *buff_ = (unsigned char*) realloc (*buff_, maxbuffsize_);
        zmq_assert (*buff_);
    }

    //  If there are no subnodes in the trie, return.
    if (count == 0)
        return;

    //  If there's one subnode (optimisation).
    if (count == 1) {
        (*buff_) [buffsize_] = min;
        buffsize_++;
        next.node->apply_helper (buff_, buffsize_, maxbuffsize_, func_, arg_);
        return;
    }

    //  If there are multiple subnodes.
    for (unsigned short c = 0; c != count; c++) {
        (*buff_) [buffsize_] = min + c;
        if (next.table [c])
            next.table [c]->apply_helper (buff_, buffsize_ + 1, maxbuffsize_,
                func_, arg_);
    }
}

bool zmq::trie_t::is_redundant () const
{
    return refcnt == 0 && live_nodes == 0;
}