Fix #513: Improve core/js Shuffle algorithm (#519)

squint-cljs · Apr 30, 2024 · 1c4b82f · 1c4b82f
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 [Squint](https://github.com/squint-cljs/squint): Light-weight ClojureScript dialect
 
+## Unreleased
+
+- [#513](https://github.com/squint-cljs/squint/issues/513): Fix `shuffle` core function random distribution and performances
+
 ## v0.7.105 (2024-04-15)
 
 - [#509](https://github.com/squint-cljs/squint/issues/509): Optimization: use arrow fn for implicit IIFE when possible

diff --git a/src/squint/core.js b/src/squint/core.js
@@ -1849,9 +1849,16 @@ export function sort_by(keyfn, comp, coll) {
 }
 
 export function shuffle(coll) {
-  return [...coll].sort(function (_a, _b) {
-    return Math.random() - 0.5;
-  });
+  const result = [...coll];
+  let remaining = coll.length;
+  while (remaining) {
+    const i = Math.floor(Math.random() * remaining--);
+    const tmp = result[remaining];
+    result[remaining] = result[i];
+    result[i] = tmp;
+  }
+
+  return result;
 }
 
 export function some(pred, coll) {