Use StringBuilder in String.replace (2x faster)

KT-41799

libraries/stdlib/jvm/src/kotlin/text/StringsJVM.kt

@@ -61,10 +61,14 @@ public actual fun String?.equals(other: String?, ignoreCase: Boolean = false): B
  */
 @Suppress("ACTUAL_FUNCTION_WITH_DEFAULT_ARGUMENTS")
 public actual fun String.replace(oldChar: Char, newChar: Char, ignoreCase: Boolean = false): String {
-    if (!ignoreCase)
+    // prefer case-insensitive platform implementation
-        return (this as java.lang.String).replace(oldChar, newChar)
+    if (!ignoreCase) return (this as java.lang.String).replace(oldChar, newChar)
-    else
+
-        return splitToSequence(oldChar, ignoreCase = ignoreCase).joinToString(separator = newChar.toString())
+    return buildString(length) {
+        this@replace.forEach { c ->
+            append(if (c.equals(oldChar, ignoreCase)) newChar else c)
+        }
+    }
 }
 
 /**
@@ -72,9 +76,29 @@ public actual fun String.replace(oldChar: Char, newChar: Char, ignoreCase: Boole
  * with the specified [newValue] string.
  */
 @Suppress("ACTUAL_FUNCTION_WITH_DEFAULT_ARGUMENTS")
-public actual fun String.replace(oldValue: String, newValue: String, ignoreCase: Boolean = false): String =
+public actual fun String.replace(oldValue: String, newValue: String, ignoreCase: Boolean = false): String {
-    splitToSequence(oldValue, ignoreCase = ignoreCase).joinToString(separator = newValue)
+    // prefer case-insensitive platform implementation
+    if (!ignoreCase) return (this as java.lang.String).replace(oldValue, newValue)
 
+    var occurrenceIndex: Int = indexOf(oldValue, 0, ignoreCase)
+    // FAST PATH: no match
+    if (occurrenceIndex < 0) return this
+
+    val oldValueLength = oldValue.length
+    val searchStep = oldValueLength.coerceAtLeast(1)
+    val newLengthHint = length - oldValueLength + newValue.length
+    if (newLengthHint < 0) throw OutOfMemoryError()
+    val stringBuilder = StringBuilder(newLengthHint)
+
+    var i = 0
+    do {
+        stringBuilder.append(this, i, occurrenceIndex).append(newValue)
+        i = occurrenceIndex + oldValueLength
+        if (occurrenceIndex >= length) break
+        occurrenceIndex = indexOf(oldValue, occurrenceIndex + searchStep, ignoreCase)
+    } while (occurrenceIndex > 0)
+    return stringBuilder.append(this, i, length).toString()
+}
 
 /**
  * Returns a new string with the first occurrence of [oldChar] replaced with [newChar].