vm: implement local slot storage for fast lookup

vm/src/main/kotlin/gay/pizza/pork/vm/InternalMachine.kt

@@ -13,8 +13,8 @@ class InternalMachine(val world: CompiledWorld, val nativeRegistry: NativeRegist
 
   private var inst: UInt = 0u
   private val stack = mutableListOf<Any>()
-  private val locals = mutableListOf<MutableMap<UInt, Any>>(
-    mutableMapOf()
+  private val locals = mutableListOf(
+    LocalSlots()
   )
   private val callStack = mutableListOf(0u)
   private val returnAddressStack = mutableListOf<UInt>()
@@ -32,7 +32,7 @@ class InternalMachine(val world: CompiledWorld, val nativeRegistry: NativeRegist
   }
 
   fun pushScope() {
-    locals.add(mutableMapOf())
+    locals.add(LocalSlots())
   }
 
   fun popScope() {
@@ -43,14 +43,13 @@ class InternalMachine(val world: CompiledWorld, val nativeRegistry: NativeRegist
     val constant = world.constantPool.constants[id.toInt()]
     when (constant.tag) {
       ConstantTag.String -> push(String(constant.value))
-      else -> throw VirtualMachineException("Unknown Constant Tag: ${constant.tag.name}")
+      else -> throw VirtualMachineException("Unknown constant tag: ${constant.tag.name}")
     }
   }
 
   fun localAt(id: UInt): Any {
     val localSet = locals.last()
-    return localSet[id] ?:
-      throw VirtualMachineException("Attempted to load local $id but it was not stored.")
+    return localSet.load(id)
   }
 
   fun loadLocal(id: UInt) {
@@ -60,7 +59,7 @@ class InternalMachine(val world: CompiledWorld, val nativeRegistry: NativeRegist
   fun storeLocal(id: UInt) {
     val localSet = locals.last()
     val value = popAnyValue()
-    localSet[id] = value
+    localSet.store(id, value)
   }
 
   fun setNextInst(value: UInt) {
@@ -106,7 +105,7 @@ class InternalMachine(val world: CompiledWorld, val nativeRegistry: NativeRegist
     callStack.clear()
     callStack.add(0u)
     locals.clear()
-    locals.add(mutableMapOf())
+    locals.add(LocalSlots())
     inst = 0u
     exitFlag = false
     autoNextInst = true

vm/src/main/kotlin/gay/pizza/pork/vm/LocalSlots.kt

@@ -0,0 +1,25 @@
+package gay.pizza.pork.vm
+
+class LocalSlots {
+  private var slots = arrayOfNulls<Any>(4)
+
+  fun load(index: UInt): Any {
+    return slots[index.toInt()]
+      ?: throw VirtualMachineException("Attempted to access local $index that is not stored")
+  }
+
+  fun store(index: UInt, value: Any) {
+    if (index >= slots.size.toUInt()) {
+      resize(index + 4u)
+    }
+    slots[index.toInt()] = value
+  }
+
+  private fun resize(count: UInt) {
+    val values = arrayOfNulls<Any>(count.toInt())
+    for ((i, value) in slots.withIndex()) {
+      values[i] = value
+    }
+    slots = values
+  }
+}

vm/src/main/kotlin/gay/pizza/pork/vm/ops/AndOpHandler.kt

@@ -7,8 +7,8 @@ import gay.pizza.pork.vm.OpHandler
 
 object AndOpHandler : OpHandler(Opcode.And) {
   override fun handle(machine: InternalMachine, op: Op) {
-    val left = machine.pop<Boolean>()
     val right = machine.pop<Boolean>()
+    val left = machine.pop<Boolean>()
     machine.push(left && right)
   }
 }

vm/src/main/kotlin/gay/pizza/pork/vm/ops/MultiplyOpHandler.kt

@@ -7,8 +7,8 @@ import gay.pizza.pork.vm.OpHandler
 
 object MultiplyOpHandler : OpHandler(Opcode.Multiply) {
   override fun handle(machine: InternalMachine, op: Op) {
-    val left = machine.pop<Int>()
     val right = machine.pop<Int>()
+    val left = machine.pop<Int>()
     machine.push(left * right)
   }
 }

vm/src/main/kotlin/gay/pizza/pork/vm/ops/OrOpHandler.kt

@@ -7,8 +7,8 @@ import gay.pizza.pork.vm.OpHandler
 
 object OrOpHandler : OpHandler(Opcode.Or) {
   override fun handle(machine: InternalMachine, op: Op) {
-    val left = machine.pop<Boolean>()
     val right = machine.pop<Boolean>()
+    val left = machine.pop<Boolean>()
     machine.push(left || right)
   }
 }