⚡ Bolt: urlEncodePath의 가비지 컬렉션(GC) 오버헤드 감소 성능 최적화

.jules/bolt.md

@@ -9,3 +9,7 @@
 ## 2024-07-26 - Intermediate String Allocations
 **Learning:** Chained `.replace()` calls on strings in Kotlin (e.g. for HTML escaping) allocate an intermediate String at each step, significantly impacting performance and garbage collection on hot paths with many elements.
 **Action:** Replace chained `.replace()` calls with a single-pass loop that iterates over characters once, lazily initializing a `StringBuilder` to append the transformed output.
+
+## 2024-07-31 - GC Overhead from String Padding in Loops
+**Learning:** Using `byte.toString(16).padStart(2, '0').toUpperCase()` for hex encoding inside a loop generates significant GC overhead due to multiple intermediate string allocations per byte.
+**Action:** Use bitwise shifts (`ushr` and `and`) with a pre-allocated array of hex characters (e.g. `val hexChars = "0123456789ABCDEF"`) to map bytes directly to hex characters, and combine it with a lazy `StringBuilder` to minimize allocations.

src/main/kotlin/html4tree/main.kt

@@ -80,10 +80,14 @@ fun String.escapeHtml(): String {
     return sb?.toString() ?: this
 }
 
+// ⚡ Bolt Performance Optimization: Reduce GC overhead in urlEncodePath
 fun String.urlEncodePath(): String {
-    val encoded = StringBuilder()
-    this.toByteArray(Charsets.UTF_8).forEach {
-        val byte = it.toInt() and 0xff
+    var encoded: StringBuilder? = null
+    val bytes = this.toByteArray(Charsets.UTF_8)
+    val hexChars = "0123456789ABCDEF"
+
+    for (i in bytes.indices) {
+        val byte = bytes[i].toInt() and 0xff
         val isUnreserved = (byte in 'A'.toInt()..'Z'.toInt()) ||
                            (byte in 'a'.toInt()..'z'.toInt()) ||
                            (byte in '0'.toInt()..'9'.toInt()) ||
@@ -92,13 +96,20 @@ fun String.urlEncodePath(): String {
                            byte == '_'.toInt() ||
                            byte == '~'.toInt()
         if (isUnreserved) {
-            encoded.append(byte.toChar())
+            encoded?.append(byte.toChar())
         } else {
+            if (encoded == null) {
+                encoded = StringBuilder(bytes.size + 16)
+                for (j in 0 until i) {
+                    encoded.append(bytes[j].toChar())
+                }
+            }
             encoded.append('%')
-            encoded.append(byte.toString(16).padStart(2, '0').toUpperCase())
+            encoded.append(hexChars[byte ushr 4])
+            encoded.append(hexChars[byte and 0x0F])
         }
     }
-    return encoded.toString()
+    return encoded?.toString() ?: this
 }
 
 fun process_ignore_file(curr_dir: File): Set<String> {