Speedup getBlockNodeIdMapping by up to factor 4 by using a fixed size mapping array

diff --git a/src/mapblock.cpp b/src/mapblock.cpp
index 95e54fb33ce849ced6f6452ee50da21e376c3d5b..8e8961e10f9bd488ffc41870fe556490cda17a95 100644 (file)
--- a/src/mapblock.cpp
+++ b/src/mapblock.cpp
@@ -452,10 +452,16 @@ s16 MapBlock::getGroundLevel(v2s16 p2d)
 */
 // List relevant id-name pairs for ids in the block using nodedef
 // Renumbers the content IDs (starting at 0 and incrementing
+// use static memory requires about 65535 * sizeof(int) ram in order to be
+// sure we can handle all content ids. But it's absolutely worth it as it's
+// a speedup of 4 for one of the major time consuming functions on storing
+// mapblocks.
+static content_t getBlockNodeIdMapping_mapping[USHRT_MAX];
 static void getBlockNodeIdMapping(NameIdMapping *nimap, MapNode *nodes,
                INodeDefManager *nodedef)
 {
-       std::map<content_t, content_t> mapping;
+       memset(getBlockNodeIdMapping_mapping, 0xFF, USHRT_MAX * sizeof(content_t));
+
        std::set<content_t> unknown_contents;
        content_t id_counter = 0;
        for(u32 i=0; i<MAP_BLOCKSIZE*MAP_BLOCKSIZE*MAP_BLOCKSIZE; i++)
@@ -464,16 +470,14 @@ static void getBlockNodeIdMapping(NameIdMapping *nimap, MapNode *nodes,
                content_t id = CONTENT_IGNORE;
 
                // Try to find an existing mapping
-               std::map<content_t, content_t>::iterator j = mapping.find(global_id);
-               if(j != mapping.end())
-               {
-                       id = j->second;
+               if (getBlockNodeIdMapping_mapping[global_id] != 0xFFFF) {
+                       id = getBlockNodeIdMapping_mapping[global_id];
                }
                else
                {
                        // We have to assign a new mapping
                        id = id_counter++;
-                       mapping.insert(std::make_pair(global_id, id));
+                       getBlockNodeIdMapping_mapping[global_id] = id;
 
                        const ContentFeatures &f = nodedef->get(global_id);
                        const std::string &name = f.name;