perf: Binary search in token store utils.search (#17066)

fasttime · web-flow · commit 9d1b8fc60cc3 · 2023-04-11T23:44:39.000+02:00
* perf: Binary search in token store `utils.search`

* Use `Math.trunc`

* Switch back to `| 0`, inline `getStartLocation`
diff --git a/lib/source-code/token-store/utils.js b/lib/source-code/token-store/utils.js
@@ -4,20 +4,6 @@
  */
 "use strict";
 
-//------------------------------------------------------------------------------
-// Helpers
-//------------------------------------------------------------------------------
-
-/**
- * Gets `token.range[0]` from the given token.
- * @param {Node|Token|Comment} token The token to get.
- * @returns {number} The start location.
- * @private
- */
-function getStartLocation(token) {
-    return token.range[0];
-}
-
 //------------------------------------------------------------------------------
 // Exports
 //------------------------------------------------------------------------------
@@ -30,9 +16,28 @@ function getStartLocation(token) {
  * @returns {number} The found index or `tokens.length`.
  */
 exports.search = function search(tokens, location) {
-    const index = tokens.findIndex(el => location <= getStartLocation(el));
+    for (let minIndex = 0, maxIndex = tokens.length - 1; minIndex <= maxIndex;) {
 
-    return index === -1 ? tokens.length : index;
+        /*
+         * Calculate the index in the middle between minIndex and maxIndex.
+         * `| 0` is used to round a fractional value down to the nearest integer: this is similar to
+         * using `Math.trunc()` or `Math.floor()`, but performance tests have shown this method to
+         * be faster.
+         */
+        const index = (minIndex + maxIndex) / 2 | 0;
+        const token = tokens[index];
+        const tokenStartLocation = token.range[0];
+
+        if (location <= tokenStartLocation) {
+            if (index === minIndex) {
+                return index;
+            }
+            maxIndex = index;
+        } else {
+            minIndex = index + 1;
+        }
+    }
+    return tokens.length;
 };
 
 /**
