diff --git a/antlr-kotlin-runtime/src/commonMain/kotlin/com/strumenta/kotlinmultiplatform/Math.kt b/antlr-kotlin-runtime/src/commonMain/kotlin/com/strumenta/kotlinmultiplatform/Math.kt
index cbbfb3a2..f19604cf 100644
--- a/antlr-kotlin-runtime/src/commonMain/kotlin/com/strumenta/kotlinmultiplatform/Math.kt
+++ b/antlr-kotlin-runtime/src/commonMain/kotlin/com/strumenta/kotlinmultiplatform/Math.kt
@@ -1,12 +1,12 @@
 package com.strumenta.kotlinmultiplatform
 
 object Math {
-  fun min(a: Int, b: Int): Int =
+  inline fun min(a: Int, b: Int): Int =
     kotlin.math.min(a, b)
 
-  fun max(a: Int, b: Int): Int =
+  inline fun max(a: Int, b: Int): Int =
     kotlin.math.max(a, b)
 
-  fun floor(d: Double): Double =
+  inline fun floor(d: Double): Double =
     kotlin.math.floor(d)
 }
diff --git a/antlr-kotlin-runtime/src/commonMain/kotlin/com/strumenta/kotlinmultiplatform/ext/String.ext.kt b/antlr-kotlin-runtime/src/commonMain/kotlin/com/strumenta/kotlinmultiplatform/ext/String.ext.kt
new file mode 100644
index 00000000..7a8fa960
--- /dev/null
+++ b/antlr-kotlin-runtime/src/commonMain/kotlin/com/strumenta/kotlinmultiplatform/ext/String.ext.kt
@@ -0,0 +1,14 @@
+package com.strumenta.kotlinmultiplatform.ext
+
+fun String.codePointIndices(): IntArray {
+  val intArray = IntArray(length)
+  var p = 0
+
+  for (i in indices) {
+    if (!hasSurrogatePairAt(i - 1)) {
+      intArray[p++] = i
+    }
+  }
+
+  return intArray.copyOfRange(0, p)
+}
diff --git a/antlr-kotlin-runtime/src/commonMain/kotlin/org/antlr/v4/kotlinruntime/StringCharStream.kt b/antlr-kotlin-runtime/src/commonMain/kotlin/org/antlr/v4/kotlinruntime/StringCharStream.kt
index 46819b37..be7a9106 100644
--- a/antlr-kotlin-runtime/src/commonMain/kotlin/org/antlr/v4/kotlinruntime/StringCharStream.kt
+++ b/antlr-kotlin-runtime/src/commonMain/kotlin/org/antlr/v4/kotlinruntime/StringCharStream.kt
@@ -2,76 +2,48 @@ package org.antlr.v4.kotlinruntime
 
 import com.strumenta.kotlinmultiplatform.Math
 import com.strumenta.kotlinmultiplatform.assert
+import com.strumenta.kotlinmultiplatform.ext.codePointIndices
 import org.antlr.v4.kotlinruntime.misc.Interval
 
-internal fun String.codePointIndices(): IntArray {
-  return (0 until length).mapNotNull { index ->
-    if (hasSurrogatePairAt(index - 1)) {
-      null
-    } else {
-      index
-    }
-  }.toIntArray()
-}
-
-private fun toCodePoint(high: Char, low: Char): Int {
-  return high.toInt().shl(10) + low.toInt() + -56613888
-}
-
 class StringCharStream(private val source: String, override val sourceName: String) : CharStream {
   private val codePointIndices = source.codePointIndices()
   private val size = codePointIndices.size
-  private var position: Int = 0
-
-  private fun codePoint(index: Int): Int {
-    return if (index in 0 until size) {
-      val char = source[codePointIndices[index]]
-      if (char.isHighSurrogate()) {
-        if (index + 1 in 0 until size) {
-          val low = source[codePointIndices[index] + 1]
-          toCodePoint(char, low)
-        } else {
-          IntStream.EOF
-        }
-      } else {
-        char.toInt()
-      }
-    } else {
-      IntStream.EOF
-    }
-  }
+  private var position = 0
 
   override fun consume() {
     if (size - position == 0) {
       assert(LA(1) == IntStream.EOF)
       throw IllegalStateException("cannot consume EOF")
     }
-    position += 1
-  }
 
-  override fun index(): Int {
-    return position
+    position++
   }
 
-  override fun size(): Int {
-    return size
-  }
+  override fun index(): Int =
+    position
 
-  /** mark/release do nothing; we have entire buffer  */
-  override fun mark(): Int {
-    return -1
-  }
+  override fun size(): Int =
+    size
 
+  /**
+   * Does nothing, as we have the entire buffer.
+   */
+  override fun mark(): Int =
+    -1
+
+  /**
+   * Does nothing, as we have the entire buffer.
+   */
   override fun release(marker: Int) {
+    // Noop
   }
 
   override fun seek(index: Int) {
     position = index
   }
 
-  override fun toString(): String {
-    return getText(Interval.of(0, size - 1))
-  }
+  override fun toString(): String =
+    getText(Interval.of(0, size - 1))
 
   override fun getText(interval: Interval): String {
     val startIndex = Math.min(interval.a, size)
@@ -79,13 +51,33 @@ class StringCharStream(private val source: String, override val sourceName: Stri
     return source.substring(codePointIndices[startIndex], codePointIndices[endIndex] + 1)
   }
 
-  override fun LA(i: Int): Int {
-    return when {
+  override fun LA(i: Int): Int =
+    when {
       i < 0 -> codePoint(position + i)
       i > 0 -> codePoint(position + i - 1)
-      else ->
-        // Undefined
-        return 0
+      // Undefined
+      else -> 0
+    }
+
+  private fun codePoint(index: Int): Int {
+    if (index !in 0..<size) {
+      return IntStream.EOF
+    }
+
+    val char = source[codePointIndices[index]]
+
+    if (char.isHighSurrogate()) {
+      if (index + 1 in 0..<size) {
+        val low = source[codePointIndices[index] + 1]
+        return toCodePoint(char, low)
+      }
+
+      return IntStream.EOF
     }
+
+    return char.code
   }
+
+  private fun toCodePoint(high: Char, low: Char): Int =
+    (high.code shl 10) + low.code + (-56613888)
 }
diff --git a/antlr-kotlin-runtime/src/commonTest/kotlin/org/antlr/v4/kotlinruntime/StringCharStreamTest.kt b/antlr-kotlin-runtime/src/commonTest/kotlin/org/antlr/v4/kotlinruntime/StringCharStreamTest.kt
index 37c67399..fb1e6cc8 100644
--- a/antlr-kotlin-runtime/src/commonTest/kotlin/org/antlr/v4/kotlinruntime/StringCharStreamTest.kt
+++ b/antlr-kotlin-runtime/src/commonTest/kotlin/org/antlr/v4/kotlinruntime/StringCharStreamTest.kt
@@ -1,6 +1,7 @@
 package org.antlr.v4.kotlinruntime
 
 import BaseTest
+import com.strumenta.kotlinmultiplatform.ext.codePointIndices
 import org.antlr.v4.kotlinruntime.misc.Interval
 import kotlin.test.Test