AStar.c

/*
 Copyright (c) 2012, Sean Heber. All rights reserved.
 
 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions are met:
 
 1. Redistributions of source code must retain the above copyright
 notice, this list of conditions and the following disclaimer.
 
 2. Redistributions in binary form must reproduce the above copyright notice,
 this list of conditions and the following disclaimer in the documentation
 and/or other materials provided with the distribution.
 
 3. Neither the name of Sean Heber nor the names of its contributors may
 be used to endorse or promote products derived from this software without
 specific prior written permission.
 
 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 DISCLAIMED. IN NO EVENT SHALL SEAN HEBER BE LIABLE FOR ANY DIRECT,
 INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
 OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "AStar.h"
#include <math.h>
#include <string.h>

struct __ASNeighborList {
    const ASPathNodeSource *source;
    size_t capacity;
    size_t count;
    float *costs;
    void *nodeKeys;
};

struct __ASPath {
    size_t nodeSize;
    size_t count;
    float cost;
    int8_t nodeKeys[];
};

typedef struct {
    unsigned isClosed:1;
    unsigned isOpen:1;
    unsigned isGoal:1;
    unsigned hasParent:1;
    unsigned hasEstimatedCost:1;
    float estimatedCost;
    float cost;
    size_t openIndex;
    size_t parentIndex;
    int8_t nodeKey[];
} NodeRecord;

struct __VisitedNodes {
    const ASPathNodeSource *source;
    void *context;
    size_t nodeRecordsCapacity;
    size_t nodeRecordsCount;
    void *nodeRecords;
    size_t *nodeRecordsIndex;           // array of nodeRecords indexes, kept sorted by nodeRecords[i]->nodeKey using source->nodeComparator
    size_t openNodesCapacity;
    size_t openNodesCount;
    size_t *openNodes;                  // binary heap of nodeRecords indexes, sorted by the nodeRecords[i]->rank
};
typedef struct __VisitedNodes *VisitedNodes;

typedef struct {
    VisitedNodes nodes;
    size_t index;
} Node;

static const Node NodeNull = {NULL, -1};

/********************************************/

static inline VisitedNodes VisitedNodesCreate(const ASPathNodeSource *source, void *context)
{
    VisitedNodes nodes = calloc(1, sizeof(struct __VisitedNodes));
    nodes->source = source;
    nodes->context = context;
    return nodes;
}

static inline void VisitedNodesDestroy(VisitedNodes visitedNodes)
{
    free(visitedNodes->nodeRecordsIndex);
    free(visitedNodes->nodeRecords);
    free(visitedNodes->openNodes);
    free(visitedNodes);
}

static inline int NodeIsNull(Node n)
{
    return (n.nodes == NodeNull.nodes) && (n.index == NodeNull.index);
}

static inline Node NodeMake(VisitedNodes nodes, size_t index)
{
    return (Node){nodes, index};
}

static inline NodeRecord *NodeGetRecord(Node node)
{
    return node.nodes->nodeRecords + (node.index * (node.nodes->source->nodeSize + sizeof(NodeRecord)));
}

static inline void *GetNodeKey(Node node)
{
    return NodeGetRecord(node)->nodeKey;
}

static inline int NodeIsInOpenSet(Node n)
{
    return NodeGetRecord(n)->isOpen;
}

static inline int NodeIsInClosedSet(Node n)
{
    return NodeGetRecord(n)->isClosed;
}

static inline void RemoveNodeFromClosedSet(Node n)
{
    NodeGetRecord(n)->isClosed = 0;
}

static inline void AddNodeToClosedSet(Node n)
{
    NodeGetRecord(n)->isClosed = 1;
}

static inline float GetNodeRank(Node n)
{
    NodeRecord *record = NodeGetRecord(n);
    return record->estimatedCost + record->cost;
}

static inline float GetNodeCost(Node n)
{
    return NodeGetRecord(n)->cost;
}

static inline float GetNodeEstimatedCost(Node n)
{
    return NodeGetRecord(n)->estimatedCost;
}

static inline void SetNodeEstimatedCost(Node n, float estimatedCost)
{
    NodeRecord *record = NodeGetRecord(n);
    record->estimatedCost = estimatedCost;
    record->hasEstimatedCost = 1;
}

static inline int NodeHasEstimatedCost(Node n)
{
    return NodeGetRecord(n)->hasEstimatedCost;
}

static inline void SetNodeIsGoal(Node n)
{
    if (!NodeIsNull(n)) {
        NodeGetRecord(n)->isGoal = 1;
    }
}

static inline int NodeIsGoal(Node n)
{
    return !NodeIsNull(n) && NodeGetRecord(n)->isGoal;
}

static inline Node GetParentNode(Node n)
{
    NodeRecord *record = NodeGetRecord(n);
    if (record->hasParent) {
        return NodeMake(n.nodes, record->parentIndex);
    } else {
        return NodeNull;
    }
}

static inline int NodeRankCompare(Node n1, Node n2)
{
    const float rank1 = GetNodeRank(n1);
    const float rank2 = GetNodeRank(n2);
    if (rank1 < rank2) {
        return -1;
    } else if (rank1 > rank2) {
        return 1;
    } else {
        return 0;
    }
}

static inline float GetPathCostHeuristic(Node a, Node b)
{
    if (a.nodes->source->pathCostHeuristic && !NodeIsNull(a) && !NodeIsNull(b)) {
        return a.nodes->source->pathCostHeuristic(GetNodeKey(a), GetNodeKey(b), a.nodes->context);
    } else {
        return 0;
    }
}

static inline int NodeKeyCompare(Node node, void *nodeKey)
{
    if (node.nodes->source->nodeComparator) {
        return node.nodes->source->nodeComparator(GetNodeKey(node), nodeKey, node.nodes->context);
    } else {
        return memcmp(GetNodeKey(node), nodeKey, node.nodes->source->nodeSize);
    }
}

static inline Node GetNode(VisitedNodes nodes, void *nodeKey)
{
    if (!nodeKey) {
        return NodeNull;
    }
    
    // looks it up in the index, if it's not found it inserts a new record in the sorted index and the nodeRecords array and returns a reference to it
    size_t first = 0;

    if (nodes->nodeRecordsCount > 0) {
        size_t last = nodes->nodeRecordsCount-1;

        while (first <= last) {
            const size_t mid = (first + last) / 2;
            const int comp = NodeKeyCompare(NodeMake(nodes, nodes->nodeRecordsIndex[mid]), nodeKey);

            if (comp < 0) {
                first = mid + 1;
            } else if (comp > 0 && mid > 0) {
                last = mid - 1;
            } else if (comp > 0) {
                break;
            } else {
                return NodeMake(nodes, nodes->nodeRecordsIndex[mid]);
            }
        }
    }
    
    if (nodes->nodeRecordsCount == nodes->nodeRecordsCapacity) {
        nodes->nodeRecordsCapacity = 1 + (nodes->nodeRecordsCapacity * 2);
        nodes->nodeRecords = realloc(nodes->nodeRecords, nodes->nodeRecordsCapacity * (sizeof(NodeRecord) + nodes->source->nodeSize));
        nodes->nodeRecordsIndex = realloc(nodes->nodeRecordsIndex, nodes->nodeRecordsCapacity * sizeof(size_t));
    }
    
    Node node = NodeMake(nodes, nodes->nodeRecordsCount);
    nodes->nodeRecordsCount++;
    
    memmove(&nodes->nodeRecordsIndex[first+1], &nodes->nodeRecordsIndex[first], (nodes->nodeRecordsCapacity - first - 1) * sizeof(size_t));
    nodes->nodeRecordsIndex[first] = node.index;
    
    NodeRecord *record = NodeGetRecord(node);
    memset(record, 0, sizeof(NodeRecord));
    memcpy(record->nodeKey, nodeKey, nodes->source->nodeSize);

    return node;
}

static inline void SwapOpenSetNodesAtIndexes(VisitedNodes nodes, size_t index1, size_t index2)
{
    if (index1 != index2) {
        NodeRecord *record1 = NodeGetRecord(NodeMake(nodes, nodes->openNodes[index1]));
        NodeRecord *record2 = NodeGetRecord(NodeMake(nodes, nodes->openNodes[index2]));
        
        const size_t tempOpenIndex = record1->openIndex;
        record1->openIndex = record2->openIndex;
        record2->openIndex = tempOpenIndex;
        
        const size_t tempNodeIndex = nodes->openNodes[index1];
        nodes->openNodes[index1] = nodes->openNodes[index2];
        nodes->openNodes[index2] = tempNodeIndex;
    }
}

static inline void DidRemoveFromOpenSetAtIndex(VisitedNodes nodes, size_t index)
{
    size_t smallestIndex = index;
    
    do {
        if (smallestIndex != index) {
            SwapOpenSetNodesAtIndexes(nodes, smallestIndex, index);
            index = smallestIndex;
        }

        const size_t leftIndex = (2 * index) + 1;
        const size_t rightIndex = (2 * index) + 2;
        
        if (leftIndex < nodes->openNodesCount && NodeRankCompare(NodeMake(nodes, nodes->openNodes[leftIndex]), NodeMake(nodes, nodes->openNodes[smallestIndex])) < 0) {
            smallestIndex = leftIndex;
        }
        
        if (rightIndex < nodes->openNodesCount && NodeRankCompare(NodeMake(nodes, nodes->openNodes[rightIndex]), NodeMake(nodes, nodes->openNodes[smallestIndex])) < 0) {
            smallestIndex = rightIndex;
        }
    } while (smallestIndex != index);
}

static inline void RemoveNodeFromOpenSet(Node n)
{
    NodeRecord *record = NodeGetRecord(n);

    if (record->isOpen) {
        record->isOpen = 0;
        n.nodes->openNodesCount--;
        
        const size_t index = record->openIndex;
        SwapOpenSetNodesAtIndexes(n.nodes, index, n.nodes->openNodesCount);
        DidRemoveFromOpenSetAtIndex(n.nodes, index);
    }
}

static inline void DidInsertIntoOpenSetAtIndex(VisitedNodes nodes, size_t index)
{
    while (index > 0) {
        const size_t parentIndex = floorf((index-1) / 2);
        
        if (NodeRankCompare(NodeMake(nodes, nodes->openNodes[parentIndex]), NodeMake(nodes, nodes->openNodes[index])) < 0) {
            break;
        } else {
            SwapOpenSetNodesAtIndexes(nodes, parentIndex, index);
            index = parentIndex;
        }
    }
}

static inline void AddNodeToOpenSet(Node n, float cost, Node parent)
{
    NodeRecord *record = NodeGetRecord(n);

    if (!NodeIsNull(parent)) {
        record->hasParent = 1;
        record->parentIndex = parent.index;
    } else {
        record->hasParent = 0;
    }

    if (n.nodes->openNodesCount == n.nodes->openNodesCapacity) {
        n.nodes->openNodesCapacity = 1 + (n.nodes->openNodesCapacity * 2);
        n.nodes->openNodes = realloc(n.nodes->openNodes, n.nodes->openNodesCapacity * sizeof(size_t));
    }

    const size_t openIndex = n.nodes->openNodesCount;
    n.nodes->openNodes[openIndex] = n.index;
    n.nodes->openNodesCount++;

    record->openIndex = openIndex;
    record->isOpen = 1;
    record->cost = cost;

    DidInsertIntoOpenSetAtIndex(n.nodes, openIndex);
}

static inline int HasOpenNode(VisitedNodes nodes)
{
    return nodes->openNodesCount > 0;
}

static inline Node GetOpenNode(VisitedNodes nodes)
{
    return NodeMake(nodes, nodes->openNodes[0]);
}

static inline ASNeighborList NeighborListCreate(const ASPathNodeSource *source)
{
    ASNeighborList list = calloc(1, sizeof(struct __ASNeighborList));
    list->source = source;
    return list;
}

static inline void NeighborListDestroy(ASNeighborList list)
{
    free(list->costs);
    free(list->nodeKeys);
    free(list);
}

static inline float NeighborListGetEdgeCost(ASNeighborList list, size_t index)
{
    return list->costs[index];
}

static void *NeighborListGetNodeKey(ASNeighborList list, size_t index)
{
    return list->nodeKeys + (index * list->source->nodeSize);
}

/********************************************/

void ASNeighborListAdd(ASNeighborList list, void *node, float edgeCost)
{
    if (list->count == list->capacity) {
        list->capacity = 1 + (list->capacity * 2);
        list->costs = realloc(list->costs, sizeof(float) * list->capacity);
        list->nodeKeys = realloc(list->nodeKeys, list->source->nodeSize * list->capacity);
    }
    list->costs[list->count] = edgeCost;
    memcpy(list->nodeKeys + (list->count * list->source->nodeSize), node, list->source->nodeSize);
    list->count++;
}

ASPath ASPathCreate(const ASPathNodeSource *source, void *context, void *startNodeKey, void *goalNodeKey)
{
    if (!startNodeKey || !source || !source->nodeNeighbors || source->nodeSize == 0) {
        return NULL;
    }
    
    VisitedNodes visitedNodes = VisitedNodesCreate(source, context);
    ASNeighborList neighborList = NeighborListCreate(source);
    Node current = GetNode(visitedNodes, startNodeKey);
    Node goalNode = GetNode(visitedNodes, goalNodeKey);
    ASPath path = NULL;
    
    // mark the goal node as the goal
    SetNodeIsGoal(goalNode);
    
    // set the starting node's estimate cost to the goal and add it to the open set
    SetNodeEstimatedCost(current,  GetPathCostHeuristic(current, goalNode));
    AddNodeToOpenSet(current, 0, NodeNull);
    
    // perform the A* algorithm
    while (HasOpenNode(visitedNodes) && !NodeIsGoal((current = GetOpenNode(visitedNodes)))) {
        if (source->earlyExit) {
            const int shouldExit = source->earlyExit(visitedNodes->nodeRecordsCount, GetNodeKey(current), goalNodeKey, context);

            if (shouldExit > 0) {
                SetNodeIsGoal(current);
                break;
            } else if (shouldExit < 0) {
                break;
            }
        }
        
        RemoveNodeFromOpenSet(current);
        AddNodeToClosedSet(current);
        
        neighborList->count = 0;
        source->nodeNeighbors(neighborList, GetNodeKey(current), context);

        for (size_t n=0; n<neighborList->count; n++) {
            const float cost = GetNodeCost(current) + NeighborListGetEdgeCost(neighborList, n);
            Node neighbor = GetNode(visitedNodes, NeighborListGetNodeKey(neighborList, n));
            
            if (!NodeHasEstimatedCost(neighbor)) {
                SetNodeEstimatedCost(neighbor, GetPathCostHeuristic(neighbor, goalNode));
            }
            
            if (NodeIsInOpenSet(neighbor) && cost < GetNodeCost(neighbor)) {
                RemoveNodeFromOpenSet(neighbor);
            }
            
            if (NodeIsInClosedSet(neighbor) && cost < GetNodeCost(neighbor)) {
                RemoveNodeFromClosedSet(neighbor);
            }
            
            if (!NodeIsInOpenSet(neighbor) && !NodeIsInClosedSet(neighbor)) {
                AddNodeToOpenSet(neighbor, cost, current);
            }
        }
    }
    
    if (NodeIsNull(goalNode)) {
        SetNodeIsGoal(current);
    }
    
    if (NodeIsGoal(current)) {
        size_t count = 0;
        Node n = current;
        
        while (!NodeIsNull(n)) {
            count++;
            n = GetParentNode(n);
        }
        
        path = malloc(sizeof(struct __ASPath) + (count * source->nodeSize));
        path->nodeSize = source->nodeSize;
        path->count = count;
        path->cost = GetNodeCost(current);
        
        n = current;
        for (size_t i=count; i>0; i--) {
            memcpy(path->nodeKeys + ((i - 1) * source->nodeSize), GetNodeKey(n), source->nodeSize);
            n = GetParentNode(n);
        }
    }
    
    NeighborListDestroy(neighborList);
    VisitedNodesDestroy(visitedNodes);

    return path;
}

void ASPathDestroy(ASPath path)
{
    free(path);
}

ASPath ASPathCopy(ASPath path)
{
    if (path) {
        const size_t size = sizeof(struct __ASPath) + (path->count * path->nodeSize);
        ASPath newPath = malloc(size);
        memcpy(newPath, path, size);
        return newPath;
    } else {
        return NULL;
    }
}

float ASPathGetCost(ASPath path)
{
    return path? path->cost : INFINITY;
}

size_t ASPathGetCount(ASPath path)
{
    return path? path->count : 0;
}

void *ASPathGetNode(ASPath path, size_t index)
{
    return (path && index < path->count)? (path->nodeKeys + (index * path->nodeSize)) : NULL;
}