Optimized getMovementToTilesAtPosition tilesToIgnore to a bitset instead of a hashset, saving 7.4% of next turn calculation time!

core/src/com/unciv/logic/map/HexMath.kt

@@ -232,12 +232,16 @@ object HexMath {
 
     /** Get number of hexes from [origin] to [destination] _without respecting world-wrap_ */
     fun getDistance(origin: Vector2, destination: Vector2): Int {
-        val relativeX = origin.x - destination.x
+        return getDistance(origin.x.toInt(), origin.y.toInt(), destination.x.toInt(), destination.y.toInt())
-        val relativeY = origin.y - destination.y
+    }
+    
+    fun getDistance(originX: Int, originY: Int, destinationX: Int, destinationY: Int): Int {
+        val relativeX = originX - destinationX
+        val relativeY = originY - destinationY
         return if (relativeX * relativeY >= 0)
-            max(abs(relativeX), abs(relativeY)).toInt()
+            max(abs(relativeX), abs(relativeY))
         else
-            (abs(relativeX) + abs(relativeY)).toInt()
+            (abs(relativeX) + abs(relativeY))
     }
 
     private val clockPositionToHexVectorMap: Map<Int, Vector2> = mapOf(
@@ -296,4 +300,40 @@ object HexMath {
             return min(getDistance(vector, Vector2(1f, radius.toFloat())), getDistance(vector, Vector2(-radius.toFloat(), -1f)))
         }
     }
+
+    /**
+     * The goal here is to map from hexagonal positions (centered on 0,0) to positive integers (starting from 0) so we can replace hashmap/hashset with arrays/bitsets
+     * Places 1-6 are ring 1, 7-18 are ring 2, etc.
+     */
+    fun getZeroBasedIndex(x: Int, y: Int): Int {
+        if (x == 0 && y == 0) return 0
+        val ring = getDistance(0,0, x, y)
+        val ringStart = 1 + 6 * ring * (ring - 1) / 2 // 1 for the center tile, then 6 for each ring
+        
+        // total number of elements in the ring is 6 * ring
+        
+        // We divide the ring into its 6 edges, each of which can be determined by an equality comparison
+        // Each edge has a start index, a variable from 0 to the number of elements in that edge
+        val positionInRing = when (ring) {
+            y -> 0 /* start index*/ + x /*variable*/    // contains `ring+1` elements
+            x -> ring + 1 /* start index */ + y /*variable*/ // contains `ring` elements - 1 already taken by x=y=ring above
+            -x -> 2 * ring + 1 /* start index */ -y /*variable*/ // contains `ring+1` elements
+            -y -> 3 * ring + 2 /*start index*/ -x /*variable*/ // contains `ring` elements - 1 already taken by -x=-y=ring above
+            x-y -> 4 * ring + 2 /* start index */ +x-1 /*variable*/ // contains `ring-1` elements. -1 because x=0 is already taken by ring=-y above
+            y-x -> 5 * ring + 1 /* start index */ +y-1 /*variable*/ // contains `ring-1` elements. -1 because y=0 is already taken by ring=-x above
+            else -> throw Exception("How???")
+        }
+        return ringStart + positionInRing
+    }
+    
+    // Much simpler to understand, passes same tests, but ~5x slower than the above
+    fun mapRelativePositionToPositiveIntRedblob(x: Int, y: Int): Int {
+        if (x == 0 && y == 0) return 0
+        val ring = getDistance(0,0, x, y)
+        val ringStart = 1 + 6 * ring * (ring - 1) / 2 // 1 for the center tile, then 6 for each ring
+        val vectorsInRing = getVectorsAtDistance(Vector2.Zero, ring, ring, false)
+        val positionInRing = vectorsInRing.indexOf(Vector2(x.toFloat(), y.toFloat()))
+        return ringStart + positionInRing
+    }
+
 }

core/src/com/unciv/logic/map/TileMap.kt

@@ -516,6 +516,7 @@ class TileMap(initialCapacity: Int = 10) : IsPartOfGameInfoSerialization {
             // looks at tileMatrix. Thus filling Tiles into tileMatrix and setting their
             // transients in the same loop will leave incomplete cached `neighbors`.
             tileInfo.tileMap = this
+            tileInfo.zeroBasedIndex = HexMath.getZeroBasedIndex(tileInfo.position.x.toInt(), tileInfo.position.y.toInt())
             tileInfo.ruleset = this.ruleset!!
             tileInfo.setTerrainTransients()
             tileInfo.setUnitTransients(setUnitCivTransients)

core/src/com/unciv/logic/map/mapunit/movement/UnitMovement.kt

@@ -11,6 +11,7 @@ import com.unciv.logic.map.tile.Tile
 import com.unciv.models.UnitActionType
 import com.unciv.models.ruleset.unique.UniqueType
 import com.unciv.ui.components.UnitMovementMemoryType
+import java.util.BitSet
 
 
 class UnitMovement(val unit: MapUnit) {
@@ -30,7 +31,7 @@ class UnitMovement(val unit: MapUnit) {
         position: Vector2,
         unitMovement: Float,
         considerZoneOfControl: Boolean = true,
-        tilesToIgnore: HashSet<Tile>? = null,
+        tilesToIgnoreBitset: BitSet? = null,
         passThroughCache: HashMap<Tile, Boolean> = HashMap(),
         movementCostCache: HashMap<Pair<Tile, Tile>, Float> = HashMap(),
         includeOtherEscortUnit: Boolean = true
@@ -49,12 +50,13 @@ class UnitMovement(val unit: MapUnit) {
             && unit.getOtherEscortUnit()?.currentMovement == 0f) return distanceToTiles
 
         var tilesToCheck = listOf(unitTile)
-
+        
         while (tilesToCheck.isNotEmpty()) {
             val updatedTiles = ArrayList<Tile>()
             for (tileToCheck in tilesToCheck)
                 for (neighbor in tileToCheck.neighbors) {
-                    if (tilesToIgnore?.contains(neighbor) == true) continue // ignore this tile
+                    // ignore this tile
+                    if (tilesToIgnoreBitset != null && tilesToIgnoreBitset.get(neighbor.zeroBasedIndex)) continue // ignore this tile
                     var totalDistanceToTile: Float = when {
                         !neighbor.isExplored(unit.civ) ->
                             distanceToTiles[tileToCheck]!!.totalMovement + 1f  // If we don't know then we just guess it to be 1.
@@ -131,7 +133,7 @@ class UnitMovement(val unit: MapUnit) {
         var distance = 1
         val unitMaxMovement = unit.getMaxMovement().toFloat()
         val newTilesToCheck = ArrayList<Tile>()
-        val visitedTiles: HashSet<Tile> = hashSetOf(currentTile)
+        val visitedTilesBitset = BitSet().apply { set(currentTile.zeroBasedIndex) }
         val civilization = unit.civ
 
         val passThroughCache = HashMap<Tile, Boolean>()
@@ -160,7 +162,7 @@ class UnitMovement(val unit: MapUnit) {
                         tileToCheck.position,
                         unitMaxMovement,
                         false,
-                        visitedTiles,
+                        visitedTilesBitset,
                         passThroughCache,
                         movementCostCache
                     )
@@ -203,11 +205,11 @@ class UnitMovement(val unit: MapUnit) {
             }
 
             // add newTilesToCheck to visitedTiles so we do not path over these tiles in a later iteration
-            visitedTiles.addAll(newTilesToCheck)
+            for (tile in newTilesToCheck) visitedTilesBitset.set(tile.zeroBasedIndex)
             // no need to check tiles that are surrounded by reachable tiles, only need to check the edgemost tiles.
             // Because anything we can reach from intermediate tiles, can be more easily reached by the edgemost tiles,
             // since we'll have to pass through an edgemost tile in order to reach the destination anyway
-            tilesToCheck = newTilesToCheck.filterNot { tile -> tile.neighbors.all { it in visitedTiles } }
+            tilesToCheck = newTilesToCheck.filterNot { tile -> tile.neighbors.all { visitedTilesBitset.get(it.zeroBasedIndex) } }
 
             distance++
         }

core/src/com/unciv/logic/map/tile/Tile.kt

@@ -98,6 +98,9 @@ class Tile : IsPartOfGameInfoSerialization, Json.Serializable {
     //region Transient fields
     @Transient
     lateinit var tileMap: TileMap
+    
+    @Transient
+    var zeroBasedIndex: Int = 0
 
     @Transient
     lateinit var ruleset: Ruleset  // a tile can be a tile with a ruleset, even without a map.

tests/src/com/unciv/logic/map/HexmathTests.kt

@@ -0,0 +1,30 @@
+package com.unciv.logic.map
+
+import com.badlogic.gdx.math.Vector2
+import org.junit.Assert
+import org.junit.Test
+
+
+class HexmathTests {
+    // Looks like our current movement is actually unoptimized, since it fails this test :)
+    @Test
+    fun zeroIndexed(){
+        Assert.assertEquals(0, HexMath.getZeroBasedIndex(0,0))
+    }
+
+    @Test
+    fun testMappingIsOneToOne(){
+        val seenCoordsMapping = hashSetOf<Int>()
+        for (ring in 1..100) {
+            val coords = HexMath.getVectorsAtDistance(Vector2.Zero, ring, 100, false)
+            val ringStartCoordinate = 1 + 6 * ring * (ring - 1) / 2
+            for (coord in coords) {
+                val mapping = HexMath.getZeroBasedIndex(coord.x.toInt(), coord.y.toInt())
+                Assert.assertFalse("Duplicate coords found: $coord", seenCoordsMapping.contains(mapping))
+                Assert.assertTrue("Coords $coord should be in ring $ring, actual mapping $mapping", mapping in ringStartCoordinate .. (ringStartCoordinate + 6 * ring - 1))
+
+                seenCoordsMapping.add(mapping)
+            }
+        }
+    }
+}