Implemented following control flow opcodes:

1) NOP
2) JMP
3) JMPIF
4) JMPIFNOT

pkg/vm/stack/context.go

@@ -120,6 +120,11 @@ func (c *Context) ReadUint16() uint16 {
 	return val
 }
 
+// ReadInt16 reads a int16 from the script
+func (c *Context) ReadInt16() int16 {
+	return int16(c.ReadUint16())
+}
+
 // ReadByte reads one byte from the script
 func (c *Context) ReadByte() (byte, error) {
 	byt, err := c.ReadBytes(1)
@@ -150,3 +155,13 @@ func (c *Context) readVarBytes() ([]byte, error) {
 	}
 	return c.ReadBytes(int(n))
 }
+
+// SetIP sets the instruction pointer ip to a given integer.
+// Returns an error if ip is less than -1 or greater than LenInstr.
+func (c *Context) SetIP(ip int) error {
+	if ok := ip < -1 || ip > c.LenInstr(); ok {
+		return errors.New("invalid instruction pointer")
+	}
+	c.ip = ip
+	return nil
+}

pkg/vm/vm_ops.go

@@ -5,6 +5,10 @@ import "github.com/CityOfZion/neo-go/pkg/vm/stack"
 type stackInfo func(op stack.Instruction, ctx *stack.Context, istack *stack.Invocation, rstack *stack.RandomAccess) (Vmstate, error)
 
 var opFunc = map[stack.Instruction]stackInfo{
+	stack.JMPIFNOT:    JMPIFNOT,
+	stack.JMPIF:       JMPIF,
+	stack.JMP:         JMP,
+	stack.NOP:         NOP,
 	stack.NUMEQUAL:    NumEqual,
 	stack.NUMNOTEQUAL: NumNotEqual,
 	stack.BOOLAND:     BoolAnd,

pkg/vm/vm_ops_flow.go

@@ -25,3 +25,71 @@ func RET(op stack.Instruction, ctx *stack.Context, istack *stack.Invocation, rst
 
 	return NONE, nil
 }
+
+// NOP Returns NONE VMState.
+func NOP(op stack.Instruction, ctx *stack.Context, istack *stack.Invocation, rstack *stack.RandomAccess) (Vmstate, error) {
+	return NONE, nil
+}
+
+// JMP moves the instruction pointer to an offset which is
+// calculated base on the instructionPointerOffset method.
+// Returns and error if the offset is out of range.
+func JMP(op stack.Instruction, ctx *stack.Context, istack *stack.Invocation, rstack *stack.RandomAccess) (Vmstate, error) {
+	offset := instructionPointerOffset(ctx)
+	if err := ctx.SetIP(offset); err != nil {
+		return FAULT, err
+
+	}
+
+	return NONE, nil
+}
+
+// JMPIF pops a boolean off of the stack and,
+// if the the boolean's value is true, it
+// moves the instruction pointer to an offset which is
+// calculated base on the instructionPointerOffset method.
+// Returns and error if the offset is out of range or
+// the popped item is not a boolean.
+func JMPIF(op stack.Instruction, ctx *stack.Context, istack *stack.Invocation, rstack *stack.RandomAccess) (Vmstate, error) {
+	b, err := ctx.Estack.PopBoolean()
+	if err != nil {
+		return FAULT, err
+	}
+
+	if b.Value() {
+		offset := instructionPointerOffset(ctx)
+		if err := ctx.SetIP(offset); err != nil {
+			return FAULT, err
+		}
+
+	}
+
+	return NONE, nil
+}
+
+// JMPIFNOT pops a boolean off of the stack and,
+// if the the boolean's value is false, it
+// moves the instruction pointer to an offset which is
+// calculated base on the instructionPointerOffset method.
+// Returns and error if the offset is out of range or
+// the popped item is not a boolean.
+func JMPIFNOT(op stack.Instruction, ctx *stack.Context, istack *stack.Invocation, rstack *stack.RandomAccess) (Vmstate, error) {
+	b, err := ctx.Estack.PopBoolean()
+	if err != nil {
+		return FAULT, err
+	}
+
+	if !b.Value() {
+		offset := instructionPointerOffset(ctx)
+		if err := ctx.SetIP(offset); err != nil {
+			return FAULT, err
+		}
+
+	}
+
+	return NONE, nil
+}
+
+func instructionPointerOffset(ctx *stack.Context) int {
+	return ctx.IP() + int(ctx.ReadInt16()) - 3
+}

pkg/vm/vm_ops_flow_test.go

@@ -0,0 +1,168 @@
+package vm
+
+import (
+	"math/big"
+	"testing"
+
+	"github.com/CityOfZion/neo-go/pkg/vm/stack"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNopOp(t *testing.T) {
+
+	v := VM{}
+
+	a, err := stack.NewInt(big.NewInt(10))
+	assert.Nil(t, err)
+
+	ctx := stack.NewContext([]byte{})
+	ctx.Estack.Push(a)
+
+	v.executeOp(stack.NOP, ctx)
+
+	// Stack should have one item
+	assert.Equal(t, 1, ctx.Estack.Len())
+
+	item, err := ctx.Estack.PopInt()
+	assert.Nil(t, err)
+
+	assert.Equal(t, int64(10), item.Value().Int64())
+}
+
+func TestJmpOp(t *testing.T) {
+
+	v := VM{}
+
+	a, err := stack.NewInt(big.NewInt(10))
+	assert.Nil(t, err)
+
+	ctx := stack.NewContext([]byte{5, 0, 2, 3, 4})
+	ctx.Estack.Push(a)
+
+	// ctx.ip = -1
+	// ctx.IP() = ctx.ip + 1
+	assert.Equal(t, 0, ctx.IP())
+
+	// ctx.ip will be set to offset.
+	// offset = ctx.IP() + int(ctx.ReadInt16()) - 3
+	//        = 0 + 5 -3 = 2
+	v.executeOp(stack.JMP, ctx)
+
+	// Stack should have one item
+	assert.Equal(t, 1, ctx.Estack.Len())
+
+	// ctx.IP() = ctx.ip + 1
+	assert.Equal(t, 3, ctx.IP())
+}
+
+// test JMPIF instruction with true boolean
+// on top of the stack
+func TestJmpIfOp1(t *testing.T) {
+
+	v := VM{}
+
+	a := stack.NewBoolean(true)
+
+	ctx := stack.NewContext([]byte{5, 0, 2, 3, 4})
+	ctx.Estack.Push(a)
+
+	// ctx.ip = -1
+	// ctx.IP() = ctx.ip + 1
+	assert.Equal(t, 0, ctx.IP())
+
+	// ctx.ip will be set to offset
+	// because the there is a true boolean
+	// on top of the stack.
+	// offset = ctx.IP() + int(ctx.ReadInt16()) - 3
+	//        = 0 + 5 -3 = 2
+	v.executeOp(stack.JMPIF, ctx)
+
+	// Stack should have 0 item
+	assert.Equal(t, 0, ctx.Estack.Len())
+
+	// ctx.IP() = ctx.ip + 1
+	assert.Equal(t, 3, ctx.IP())
+}
+
+// test JMPIF instruction with false boolean
+// on top of the stack
+func TestJmpIfOp2(t *testing.T) {
+
+	v := VM{}
+
+	a := stack.NewBoolean(false)
+
+	ctx := stack.NewContext([]byte{5, 0, 2, 3, 4})
+	ctx.Estack.Push(a)
+
+	// ctx.ip = -1
+	// ctx.IP() = ctx.ip + 1
+	assert.Equal(t, 0, ctx.IP())
+
+	// nothing will happen because
+	// the value of the boolean on top of the stack
+	// is false
+	v.executeOp(stack.JMPIF, ctx)
+
+	// Stack should have 0 item
+	assert.Equal(t, 0, ctx.Estack.Len())
+
+	// ctx.IP() = ctx.ip + 1
+	assert.Equal(t, 0, ctx.IP())
+}
+
+// test JMPIFNOT instruction with true boolean
+// on top of the stack
+func TestJmpIfNotOp1(t *testing.T) {
+
+	v := VM{}
+
+	a := stack.NewBoolean(true)
+
+	ctx := stack.NewContext([]byte{5, 0, 2, 3, 4})
+	ctx.Estack.Push(a)
+
+	// ctx.ip = -1
+	// ctx.IP() = ctx.ip + 1
+	assert.Equal(t, 0, ctx.IP())
+
+	// nothing will happen because
+	// the value of the boolean on top of the stack
+	// is true
+	v.executeOp(stack.JMPIFNOT, ctx)
+
+	// Stack should have 0 item
+	assert.Equal(t, 0, ctx.Estack.Len())
+
+	// ctx.IP() = ctx.ip + 1
+	assert.Equal(t, 0, ctx.IP())
+}
+
+// test JMPIFNOT instruction with false boolean
+// on top of the stack
+func TestJmpIfNotOp2(t *testing.T) {
+
+	v := VM{}
+
+	a := stack.NewBoolean(false)
+
+	ctx := stack.NewContext([]byte{5, 0, 2, 3, 4})
+	ctx.Estack.Push(a)
+
+	// ctx.ip = -1
+	// ctx.IP() = ctx.ip + 1
+	assert.Equal(t, 0, ctx.IP())
+
+	// ctx.ip will be set to offset
+	// because the there is a false boolean
+	// on top of the stack.
+	// offset = ctx.IP() + int(ctx.ReadInt16()) - 3
+	//        = 0 + 5 -3 = 2
+	v.executeOp(stack.JMPIFNOT, ctx)
+
+	// Stack should have one item
+	assert.Equal(t, 0, ctx.Estack.Len())
+
+	// ctx.IP() = ctx.ip + 1
+	assert.Equal(t, 3, ctx.IP())
+}