misc fixes

internal/vm/vm.go

@@ -130,11 +130,19 @@ func (vm *VM) currentFrame() *Frame {
 }
 
 func (vm *VM) pushFrame(f Frame) {
+	if vm.fp >= MaxFrames {
+		panic("frame overflow")
+	}
+
 	vm.frames[vm.fp] = f
 	vm.fp++
 }
 
 func (vm *VM) popFrame() Frame {
+	if vm.fp == 0 {
+		panic("fame underflow")
+	}
+
 	vm.fp--
 	return vm.frames[vm.fp]
 }
@@ -201,6 +209,10 @@ func (vm *VM) push(o object.Object) error {
 }
 
 func (vm *VM) pop() object.Object {
+	if vm.sp == 0 {
+		panic("stack underflow")
+	}
+
 	o := vm.stack[vm.sp-1]
 	vm.sp--
 	return o
@@ -768,20 +780,22 @@ func (vm *VM) Run() (err error) {
 	if vm.Debug {
 		start := time.Now()
 		defer func() {
+			end := time.Now().Sub(start)
 			total := 0
 			opcodes := make([]code.Opcode, 0, len(opcodeFreqs))
 
-			for opcode := range opcodeFreqs {
+			for opcode, count := range opcodeFreqs {
 				opcodes = append(opcodes, opcode)
+				total += count
 			}
 
 			sort.SliceStable(opcodes, func(i, j int) bool {
 				return opcodeFreqs[opcodes[i]] > opcodeFreqs[opcodes[j]]
 			})
 
-			log.Printf("%d instructions executed in %s", total, time.Now().Sub(start))
-			log.Print("Top 10 instructions:")
-			for _, opcode := range opcodes[:10] {
+			log.Printf("%d instructions executed in %s %d/µs", total, end, total/int(end.Microseconds()))
+			log.Print("Top Instructions:")
+			for _, opcode := range opcodes[:min(len(opcodes), 10)] {
 				log.Printf("%10d %s", opcodeFreqs[opcode], opcode)
 			}
 		}()