From 34d7277eecf4dcaf3af208a0b39f69c09595387d Mon Sep 17 00:00:00 2001
From: muendlein <71090451+muendlein@users.noreply.github.com>
Date: Sun, 7 Dec 2025 23:56:17 +0100
Subject: [PATCH] Switch to non recursive quicksort (#70)

* added test

* add Bentley-McIlroy 3-way partitioning

* switch to non recursive implementation

* fixed stack handling

* rename function

* escaped ts errors + enhanced performance

* remove escaped error

* additional performance enhancement
---
 index.js | 68 ++++++++++++++++++++++++++++++++++++++++++--------------
 test.js  | 31 ++++++++++++++++++++++++++
 2 files changed, 82 insertions(+), 17 deletions(-)

diff --git a/index.js b/index.js
index d4cd431..099c464 100644
--- a/index.js
+++ b/index.js
@@ -349,12 +349,58 @@ function upperBound(value, arr) {
  * @param {number} nodeSize
  */
 function sort(values, boxes, indices, left, right, nodeSize) {
-    if (Math.floor(left / nodeSize) >= Math.floor(right / nodeSize)) return;
+    const stack = [];
+    let stackPointer = 0;
 
+    stack.push(left);
+    stackPointer++;
+    stack.push(right);
+    stackPointer++;
+
+    while (stackPointer > 0) {
+        // @ts-expect-error
+        const r = stack.pop();
+        stackPointer--;
+        const l = stack.pop();
+        stackPointer--;
+
+        // @ts-expect-error
+        if ((r - l) <= nodeSize) {
+            // @ts-expect-error
+            if (Math.floor(l / nodeSize) >= Math.floor(r / nodeSize)) continue;
+        }
+
+        // @ts-expect-error
+        const pivot = getPivot(values, l, r);
+
+        // @ts-expect-error
+        let i = l - 1;
+        // @ts-expect-error
+        let j = r + 1;
+
+        while (true) {
+            do i++; while (values[i] < pivot);
+            do j--; while (values[j] > pivot);
+            if (i >= j) break;
+            swap(values, boxes, indices, i, j);
+        }
+
+        stack.push(l, j, j + 1, r);
+        stackPointer += 4;
+    }
+}
+
+/**
+ * Determine pivot value.
+ * @param {Uint32Array} values
+ * @param {number} l
+ * @param {number} r
+ */
+function getPivot(values, l, r) {
     // apply median of three method
-    const start = values[left];
-    const mid = values[(left + right) >> 1];
-    const end = values[right];
+    const start = values[l];
+    const mid = values[(l + r) >> 1];
+    const end = values[r];
 
     let pivot = end;
 
@@ -366,19 +412,7 @@ function sort(values, boxes, indices, left, right, nodeSize) {
     } else if (x === mid) {
         pivot = Math.max(start, end);
     }
-
-    let i = left - 1;
-    let j = right + 1;
-
-    while (true) {
-        do i++; while (values[i] < pivot);
-        do j--; while (values[j] > pivot);
-        if (i >= j) break;
-        swap(values, boxes, indices, i, j);
-    }
-
-    sort(values, boxes, indices, left, j, nodeSize);
-    sort(values, boxes, indices, j + 1, right, nodeSize);
+    return pivot;
 }
 
 /**
diff --git a/test.js b/test.js
index fc3dca0..00b9844 100644
--- a/test.js
+++ b/test.js
@@ -250,4 +250,35 @@ test('quicksort should work with an inbalanced dataset', () => {
     });
 });
 
+test('quicksort should work with duplicates', () => {
+    const n = 55000 + 5500 + 7700;
+    const index = new Flatbush(n);
+
+    let x = 0;
+
+    for (let p = 0; p < 55000; p++) {
+        index.add(x, 3.0, x, 3.0);
+        x++;
+    }
+
+    for (let p = 0; p < 5500; p++) {
+        index.add(x, 4.0, x, 4.0);
+        x++;
+    }
+
+    for (let p = 0; p < 7700; p++) {
+        index.add(x, 5.0, x, 5.0);
+        x++;
+    }
+
+    index.finish();
+
+    assert.doesNotThrow(() => {
+        index.search(0.5, -1, 6.5, 1);
+    });
+});
+
+
+
+
 function compare(a, b) { return a - b; }