remove binary search for level bound

slightly improves search performance, closes #6

Author: mourner

README.md

@@ -102,13 +102,13 @@ Running `npm run bench` with Node v8.10.0:
 ```
 1000000 rectangles
 
-flatbush: 252.311ms
-1000 searches 10%: 624.059ms
-1000 searches 1%: 76.290ms
-1000 searches 0.01%: 8.923ms
-
-rbush: 1239.848ms
-1000 searches 10%: 973.296ms
-1000 searches 1%: 180.831ms
-1000 searches 0.01%: 17.746ms
+flatbush: 252.849ms
+1000 searches 10%: 617.473ms
+1000 searches 1%: 66.968ms
+1000 searches 0.01%: 7.818ms
+
+rbush: 1083.758ms
+1000 searches 10%: 920.252ms
+1000 searches 1%: 173.104ms
+1000 searches 0.01%: 19.057ms
 ```

index.js

@@ -125,12 +125,13 @@ export default class Flatbush {
         }
 
         let nodeIndex = this.data.length - 5;
+        let level = this._levelBounds.length - 1;
         const queue = [];
         const results = [];
 
         while (nodeIndex !== undefined) {
             // find the end index of the node
-            const end = Math.min(nodeIndex + this.nodeSize * 5, upperBound(nodeIndex, this._levelBounds));
+            const end = Math.min(nodeIndex + this.nodeSize * 5, this._levelBounds[level]);
 
             // search through child nodes
             for (let pos = nodeIndex; pos < end; pos += 5) {
@@ -149,31 +150,18 @@ export default class Flatbush {
 
                 } else {
                     queue.push(index); // node; add it to the search queue
+                    queue.push(level - 1);
                 }
             }
 
+            level = queue.pop();
             nodeIndex = queue.pop();
         }
 
         return results;
     }
 }
 
-// binary search for the first value in the array bigger than the given
-function upperBound(value, arr) {
-    let i = 0;
-    let j = arr.length - 1;
-    while (i < j) {
-        const m = (i + j) >> 1;
-        if (arr[m] > value) {
-            j = m;
-        } else {
-            i = m + 1;
-        }
-    }
-    return arr[i];
-}
-
 // custom quicksort that sorts bbox data alongside the hilbert values
 function sort(values, boxes, left, right) {
     if (left >= right) return;