Restrict global and function references to memory size

gen/operand.go

@@ -12,10 +12,10 @@ func randOperand(t vm.OperandNumericType) *vm.Operand {
 
 		switch op.Type {
 		case vm.GlobalMemoryIndex:
-			op.Value = RandBiasedUint64()
+			op.Value = RandBiasedUint64n(vm.GlobalMemorySize)
 
 		case vm.FunctionMemoryIndex:
-			op.Value = RandBiasedUint64()
+			op.Value = RandBiasedUint64n(vm.FunctionMemorySize)
 
 		case vm.Literal:
 			switch t {

gen/rand.go

@@ -9,6 +9,16 @@ func RandBiasedUint64() uint64 {
 	return (rand.Uint64() | 0x8000000000000000) >> rand.Intn(65)
 }
 
+// Like RandBiasedUint64() but always returns < n
+func RandBiasedUint64n(n uint64) uint64 {
+	for {
+		ret := RandBiasedUint64()
+		if ret < n {
+			return ret
+		}
+	}
+}
+
 // Generate a random int64 with an even distribution of the tuple
 // {sign, bits.Len64(math.Abs())}
 func RandBiasedInt64() uint64 {

test/gen_test.go

@@ -3,7 +3,17 @@ package test
 import "testing"
 
 import "github.com/firestuff/subcoding/gen"
+import "github.com/firestuff/subcoding/asm"
 
 func TestRandProgram(t *testing.T) {
-	gen.RandProgram()
+	for i := 0; i < 100; i++ {
+		prog := gen.RandProgram()
+
+		src, err := asm.Disassemble(prog)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		t.Log(src)
+	}
 }

vm/stackframe.go

@@ -1,5 +1,7 @@
 package vm
 
+const FunctionMemorySize = 16
+
 type stackFrame struct {
 	previousFunctionIndex    int64
 	previousInstructionIndex int64
@@ -10,6 +12,6 @@ func newStackFrame(state *State) *stackFrame {
 	return &stackFrame{
 		previousFunctionIndex:    state.functionIndex,
 		previousInstructionIndex: state.instructionIndex,
-		functionMemory:           NewMemory(16),
+		functionMemory:           NewMemory(FunctionMemorySize),
 	}
 }

vm/state.go

@@ -2,6 +2,8 @@ package vm
 
 import "fmt"
 
+const GlobalMemorySize = 16
+
 type State struct {
 	running bool
 	err     error
@@ -18,7 +20,7 @@ type State struct {
 func NewState(prog *Program) (*State, error) {
 	return &State{
 		program:      prog,
-		globalMemory: NewMemory(16),
+		globalMemory: NewMemory(GlobalMemorySize),
 	}, nil
 }