Implemented following opcodes:

1) DUP
2) NIP
3) OVER
4) PICK

pkg/vm/stack/stack.go

@@ -127,6 +127,37 @@ func (ras *RandomAccess) CopyTo(stack *RandomAccess) error {
 	return nil
 }
 
+// Set sets the n-item from the stack
+// starting from the top of the stack with the new item.
+// the n-item to replace is located at the position "len(stack)-index-1".
+func (ras *RandomAccess) Set(index uint16, item Item) error {
+	stackSize := uint16(len(ras.vals))
+	if ok := index >= stackSize; ok {
+		return errors.New("index out of range")
+	}
+
+	n := stackSize - index - 1
+	ras.vals[n] = item
+
+	return nil
+}
+
+// Remove removes the n-item from the stack
+// starting from the top of the stack. In other words
+// the n-item to remove is located at the index "len(stack)-n-1"
+func (ras *RandomAccess) Remove(n uint16) (Item, error) {
+	if int(n) >= len(ras.vals) {
+		return nil, errors.New("index out of range")
+	}
+
+	index := uint16(len(ras.vals)) - n - 1
+	item := ras.vals[index]
+
+	ras.vals = append(ras.vals[:index], ras.vals[index+1:]...)
+
+	return item, nil
+}
+
 // Convenience Functions
 
 // PopInt will remove the last stack item that was added

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.PICK:        PICK,
+	stack.OVER:        OVER,
+	stack.NIP:         NIP,
+	stack.DUP:         DUP,
 	stack.NUMEQUAL:    NumEqual,
 	stack.NUMNOTEQUAL: NumNotEqual,
 	stack.BOOLAND:     BoolAnd,

pkg/vm/vm_ops_stackmani.go

@@ -17,3 +17,67 @@ func PushNBytes(op stack.Instruction, ctx *stack.Context, istack *stack.Invocati
 	ctx.Estack.Push(ba)
 	return NONE, nil
 }
+
+// DUP duplicates the top stack item.
+// Returns an error if stack is empty.
+func DUP(op stack.Instruction, ctx *stack.Context, istack *stack.Invocation, rstack *stack.RandomAccess) (Vmstate, error) {
+
+	item, err := ctx.Estack.Peek(0)
+	if err != nil {
+		return FAULT, err
+	}
+
+	ctx.Estack.Push(item)
+
+	return NONE, nil
+}
+
+// NIP removes the second top stack item.
+// Returns error if the stack item contains
+// only one element.
+func NIP(op stack.Instruction, ctx *stack.Context, istack *stack.Invocation, rstack *stack.RandomAccess) (Vmstate, error) {
+
+	_, err := ctx.Estack.Remove(1)
+	if err != nil {
+		return FAULT, err
+	}
+
+	return NONE, nil
+}
+
+// OVER copies the second-to-top stack item onto the top.
+// Returns an error if the stack item contains
+// only one element.
+func OVER(op stack.Instruction, ctx *stack.Context, istack *stack.Invocation, rstack *stack.RandomAccess) (Vmstate, error) {
+
+	item, err := ctx.Estack.Peek(1)
+	if err != nil {
+		return FAULT, err
+	}
+
+	ctx.Estack.Push(item)
+
+	return NONE, nil
+}
+
+// PICK pops an integer n off of the stack and
+// copies the n-item starting from
+// the top of the stack onto the top stack item.
+// Returns an error if the top stack item is not an
+// integer or n-item does not exist.
+func PICK(op stack.Instruction, ctx *stack.Context, istack *stack.Invocation, rstack *stack.RandomAccess) (Vmstate, error) {
+
+	n, err := ctx.Estack.PopInt()
+	if err != nil {
+		return FAULT, err
+	}
+
+	nItem, err := ctx.Estack.Peek(uint16(n.Value().Int64()))
+	if err != nil {
+		return FAULT, err
+	}
+
+	ctx.Estack.Push(nItem)
+
+	return NONE, nil
+}

pkg/vm/vm_ops_stackmani_test.go

@@ -0,0 +1,197 @@
+package vm
+
+import (
+	"math/big"
+	"testing"
+
+	"github.com/CityOfZion/neo-go/pkg/vm/stack"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDupOp(t *testing.T) {
+
+	v := VM{}
+
+	a, err := stack.NewInt(big.NewInt(3))
+	assert.Nil(t, err)
+
+	ctx := stack.NewContext([]byte{})
+	ctx.Estack.Push(a)
+
+	v.executeOp(stack.DUP, ctx)
+
+	// Stack should have two items
+	assert.Equal(t, 2, ctx.Estack.Len())
+
+	item1, err := ctx.Estack.PopInt()
+	assert.Nil(t, err)
+
+	item2, err := ctx.Estack.PopInt()
+	assert.Nil(t, err)
+
+	assert.Equal(t, int64(3), item1.Value().Int64())
+	assert.Equal(t, int64(3), item2.Value().Int64())
+
+}
+
+func TestNipOp(t *testing.T) {
+
+	v := VM{}
+
+	a, err := stack.NewInt(big.NewInt(3))
+	assert.Nil(t, err)
+
+	b, err := stack.NewInt(big.NewInt(6))
+	assert.Nil(t, err)
+
+	c, err := stack.NewInt(big.NewInt(9))
+	assert.Nil(t, err)
+
+	ctx := stack.NewContext([]byte{})
+	ctx.Estack.Push(a).Push(b).Push(c)
+
+	v.executeOp(stack.NIP, ctx)
+
+	// Stack should have two items
+	assert.Equal(t, 2, ctx.Estack.Len())
+
+	itemC, err := ctx.Estack.PopInt()
+	assert.Nil(t, err)
+
+	itemA, err := ctx.Estack.PopInt()
+	assert.Nil(t, err)
+
+	assert.Equal(t, int64(3), itemA.Value().Int64())
+	assert.Equal(t, int64(9), itemC.Value().Int64())
+
+}
+
+func TestOverOp(t *testing.T) {
+
+	v := VM{}
+
+	a, err := stack.NewInt(big.NewInt(3))
+	assert.Nil(t, err)
+
+	b, err := stack.NewInt(big.NewInt(6))
+	assert.Nil(t, err)
+
+	ctx := stack.NewContext([]byte{})
+	ctx.Estack.Push(a).Push(b)
+
+	// OVER copies the second top stack item a
+	// onto the top stack item b.
+	// the new stack will be [a,b,a].
+	v.executeOp(stack.OVER, ctx)
+
+	// Stack should have three items
+	assert.Equal(t, 3, ctx.Estack.Len())
+
+	itemA, err := ctx.Estack.PopInt()
+	assert.Nil(t, err)
+
+	itemB, err := ctx.Estack.PopInt()
+	assert.Nil(t, err)
+
+	itemA2, err := ctx.Estack.PopInt()
+	assert.Nil(t, err)
+
+	assert.Equal(t, int64(3), itemA.Value().Int64())
+	assert.Equal(t, int64(6), itemB.Value().Int64())
+	assert.Equal(t, int64(3), itemA2.Value().Int64())
+
+}
+
+func TestPickOp(t *testing.T) {
+
+	v := VM{}
+
+	a, err := stack.NewInt(big.NewInt(3))
+	assert.Nil(t, err)
+
+	b, err := stack.NewInt(big.NewInt(6))
+	assert.Nil(t, err)
+
+	c, err := stack.NewInt(big.NewInt(9))
+	assert.Nil(t, err)
+
+	d, err := stack.NewInt(big.NewInt(2))
+	assert.Nil(t, err)
+
+	ctx := stack.NewContext([]byte{})
+	ctx.Estack.Push(a).Push(b).Push(c).Push(d)
+
+	// pop n (= d = 2) from the stack.
+	// we will copy the n-item which
+	// has index len(stack)-n-1 (= 3-2-1= 0)
+	// onto the top stack item.
+	// The final stack will be [a,b,c,a]
+	v.executeOp(stack.PICK, ctx)
+
+	// Stack should have four items
+	assert.Equal(t, 4, ctx.Estack.Len())
+
+	itemA, err := ctx.Estack.PopInt()
+	assert.Nil(t, err)
+
+	itemC, err := ctx.Estack.PopInt()
+	assert.Nil(t, err)
+
+	itemB, err := ctx.Estack.PopInt()
+	assert.Nil(t, err)
+
+	itemA2, err := ctx.Estack.PopInt()
+	assert.Nil(t, err)
+
+	assert.Equal(t, int64(3), itemA.Value().Int64())
+	assert.Equal(t, int64(9), itemC.Value().Int64())
+	assert.Equal(t, int64(6), itemB.Value().Int64())
+	assert.Equal(t, int64(3), itemA2.Value().Int64())
+
+}
+
+/*
+func TestXswapOp(t *testing.T) {
+
+	v := VM{}
+
+	sert.Nil(t, err)
+
+	ctx := stack.NewContext([]byte{})
+	ctx.Estack.Push(a).Push(b).Push(c).Push(d)
+
+	// pop n (= d = 2) from the stack.
+	// we wa, err := stack.NewInt(big.NewInt(3))
+	assert.Nil(t, err)
+
+	b, err := stack.NewInt(big.NewInt(6))
+	assert.Nil(t, err)
+
+	c, err := stack.NewInt(big.NewInt(9))
+	assert.Nil(t, err)
+
+	d, err := stack.NewInt(big.NewInt(2))
+	asill swap the n-item which
+	// is located in position len(stack)-n-1 (= 3-2-1= 0)
+	// with the top stack item.
+	// The final stack will be [c,b,a]
+	v.executeOp(stack.XSWAP, ctx)
+
+	// Stack should have three items
+	assert.Equal(t, 3, ctx.Estack.Len())
+
+	itemA, err := ctx.Estack.PopInt()
+	assert.Nil(t, err)
+
+	itemB, err := ctx.Estack.PopInt()
+	assert.Nil(t, err)
+
+	itemC, err := ctx.Estack.PopInt()
+	assert.Nil(t, err)
+
+	assert.Equal(t, int64(3), itemA.Value().Int64())
+	assert.Equal(t, int64(6), itemB.Value().Int64())
+	assert.Equal(t, int64(9), itemC.Value().Int64())
+
+}
+*/