neoneo-go/pkg/vm/stack.go

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package vm
import (
"encoding/json"
"fmt"
"math/big"
"github.com/CityOfZion/neo-go/pkg/util"
)
// Stack implementation for the neo-go virtual machine. The stack implements
// a double linked list where its semantics are first in first out.
// To simplify the implementation, internally a Stack s is implemented as a
// ring, such that &s.top is both the next element of the last element s.Back()
// and the previous element of the first element s.Top().
//
// s.Push(0)
// s.Push(1)
// s.Push(2)
//
// [ 2 ] > top
// [ 1 ]
// [ 0 ] > back
//
// s.Pop() > 2
//
// [ 1 ]
// [ 0 ]
// Element represents an element in the double linked list (the stack),
// which will hold the underlying StackItem.
type Element struct {
value StackItem
next, prev *Element
stack *Stack
}
// NewElement returns a new Element object, with its underlying value inferred
// to the corresponding type.
func NewElement(v interface{}) *Element {
return &Element{
value: makeStackItem(v),
}
}
// Next returns the next element in the stack.
func (e *Element) Next() *Element {
if elem := e.next; e.stack != nil && elem != &e.stack.top {
return elem
}
return nil
}
// Prev returns the previous element in the stack.
func (e *Element) Prev() *Element {
if elem := e.prev; e.stack != nil && elem != &e.stack.top {
return elem
}
return nil
}
// Item returns StackItem contained in the element.
func (e *Element) Item() StackItem {
return e.value
}
// Value returns value of the StackItem contained in the element.
func (e *Element) Value() interface{} {
return e.value.Value()
}
// BigInt attempts to get the underlying value of the element as a big integer.
// Will panic if the assertion failed which will be caught by the VM.
func (e *Element) BigInt() *big.Int {
switch t := e.value.(type) {
case *BigIntegerItem:
return t.value
case *BoolItem:
if t.value {
return big.NewInt(1)
}
return big.NewInt(0)
default:
b := t.Value().([]uint8)
return new(big.Int).SetBytes(util.ArrayReverse(b))
}
}
// TryBool attempts to get the underlying value of the element as a boolean.
// Returns error if can't convert value to boolean type.
func (e *Element) TryBool() (bool, error) {
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switch t := e.value.(type) {
case *BigIntegerItem:
return t.value.Int64() != 0, nil
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case *BoolItem:
return t.value, nil
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case *ArrayItem, *StructItem:
return true, nil
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case *ByteArrayItem:
for _, b := range t.value {
if b != 0 {
return true, nil
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}
}
return false, nil
case *InteropItem:
return t.value != nil, nil
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default:
return false, fmt.Errorf("can't convert to bool: " + t.String())
}
}
// Bool attempts to get the underlying value of the element as a boolean.
// Will panic if the assertion failed which will be caught by the VM.
func (e *Element) Bool() bool {
val, err := e.TryBool()
if err != nil {
panic(err)
}
return val
}
// Bytes attempts to get the underlying value of the element as a byte array.
// Will panic if the assertion failed which will be caught by the VM.
func (e *Element) Bytes() []byte {
switch t := e.value.(type) {
case *ByteArrayItem:
return t.value
case *BigIntegerItem:
return t.Bytes() // neoVM returns in LE
case *BoolItem:
if t.value {
return []byte{1}
}
// return []byte{0}
// FIXME revert when NEO 3.0 https://github.com/nspcc-dev/neo-go/issues/477
return []byte{}
default:
panic("can't convert to []byte: " + t.String())
}
}
// Array attempts to get the underlying value of the element as an array of
// other items. Will panic if the item type is different which will be caught
// by the VM.
func (e *Element) Array() []StackItem {
switch t := e.value.(type) {
case *ArrayItem:
return t.value
case *StructItem:
return t.value
default:
panic("element is not an array")
}
}
// Stack represents a Stack backed by a double linked list.
type Stack struct {
top Element
name string
len int
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itemCount map[StackItem]int
size *int
}
// NewStack returns a new stack name by the given name.
func NewStack(n string) *Stack {
s := &Stack{
name: n,
}
s.top.next = &s.top
s.top.prev = &s.top
s.len = 0
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s.itemCount = make(map[StackItem]int)
s.size = new(int)
return s
}
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// Clear clears all elements on the stack and set its length to 0.
func (s *Stack) Clear() {
s.top.next = &s.top
s.top.prev = &s.top
s.len = 0
}
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// Len returns the number of elements that are on the stack.
func (s *Stack) Len() int {
return s.len
}
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// insert inserts the element after element (at) on the stack.
func (s *Stack) insert(e, at *Element) *Element {
// If we insert an element that is already popped from this stack,
// we need to clean it up, there are still pointers referencing to it.
if e.stack == s {
e = NewElement(e.value)
}
n := at.next
at.next = e
e.prev = at
e.next = n
n.prev = e
e.stack = s
s.len++
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s.updateSizeAdd(e.value)
return e
}
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func (s *Stack) updateSizeAdd(item StackItem) {
*s.size++
s.itemCount[item]++
if s.itemCount[item] > 1 {
return
}
switch t := item.(type) {
case *ArrayItem, *StructItem:
for _, it := range item.Value().([]StackItem) {
s.updateSizeAdd(it)
}
case *MapItem:
for _, v := range t.value {
s.updateSizeAdd(v)
}
}
}
func (s *Stack) updateSizeRemove(item StackItem) {
*s.size--
if s.itemCount[item] > 1 {
s.itemCount[item]--
return
}
delete(s.itemCount, item)
switch t := item.(type) {
case *ArrayItem, *StructItem:
for _, it := range item.Value().([]StackItem) {
s.updateSizeRemove(it)
}
case *MapItem:
for _, v := range t.value {
s.updateSizeRemove(v)
}
}
}
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// InsertAt inserts the given item (n) deep on the stack.
// Be very careful using it and _always_ check both e and n before invocation
// as it will silently do wrong things otherwise.
func (s *Stack) InsertAt(e *Element, n int) *Element {
before := s.Peek(n - 1)
if before == nil {
return nil
}
return s.insert(e, before)
}
// Push pushes the given element on the stack.
func (s *Stack) Push(e *Element) {
s.insert(e, &s.top)
}
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// PushVal pushes the given value on the stack. It will infer the
// underlying StackItem to its corresponding type.
func (s *Stack) PushVal(v interface{}) {
s.Push(NewElement(v))
}
// Pop removes and returns the element on top of the stack.
func (s *Stack) Pop() *Element {
return s.Remove(s.Top())
}
// Top returns the element on top of the stack. Nil if the stack
// is empty.
func (s *Stack) Top() *Element {
if s.len == 0 {
return nil
}
return s.top.next
}
// Back returns the element at the end of the stack. Nil if the stack
// is empty.
func (s *Stack) Back() *Element {
if s.len == 0 {
return nil
}
return s.top.prev
}
// Peek returns the element (n) far in the stack beginning from
// the top of the stack.
// n = 0 => will return the element on top of the stack.
func (s *Stack) Peek(n int) *Element {
i := 0
for e := s.Top(); e != nil; e = e.Next() {
if n == i {
return e
}
i++
}
return nil
}
// RemoveAt removes the element (n) deep on the stack beginning
// from the top of the stack.
func (s *Stack) RemoveAt(n int) *Element {
return s.Remove(s.Peek(n))
}
// Remove removes and returns the given element from the stack.
func (s *Stack) Remove(e *Element) *Element {
if e == nil {
return nil
}
e.prev.next = e.next
e.next.prev = e.prev
e.next = nil // avoid memory leaks.
e.prev = nil // avoid memory leaks.
e.stack = nil
s.len--
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s.updateSizeRemove(e.value)
return e
}
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// Dup duplicates and returns the element at position n.
// Dup is used for copying elements on to the top of its own stack.
// s.Push(s.Peek(0)) // will result in unexpected behaviour.
// s.Push(s.Dup(0)) // is the correct approach.
func (s *Stack) Dup(n int) *Element {
e := s.Peek(n)
if e == nil {
return nil
}
return &Element{
value: e.value,
}
}
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// Iter iterates over all the elements int the stack, starting from the top
// of the stack.
// s.Iter(func(elem *Element) {
// // do something with the element.
// })
func (s *Stack) Iter(f func(*Element)) {
for e := s.Top(); e != nil; e = e.Next() {
f(e)
}
}
// popSigElements pops keys or signatures from the stack as needed for
// CHECKMULTISIG.
func (s *Stack) popSigElements() ([][]byte, error) {
var num int
var elems [][]byte
item := s.Pop()
if item == nil {
return nil, fmt.Errorf("nothing on the stack")
}
switch item.value.(type) {
case *ArrayItem:
num = len(item.Array())
if num < 1 {
return nil, fmt.Errorf("less than one element in the array")
}
elems = make([][]byte, num)
for k, v := range item.Array() {
b, ok := v.Value().([]byte)
if !ok {
return nil, fmt.Errorf("bad element %s", v.String())
}
elems[k] = b
}
default:
num = int(item.BigInt().Int64())
if num < 1 || num > s.Len() {
return nil, fmt.Errorf("wrong number of elements: %d", num)
}
elems = make([][]byte, num)
for i := 0; i < num; i++ {
elems[i] = s.Pop().Bytes()
}
}
return elems, nil
}
// MarshalJSON implements JSON marshalling interface.
func (s *Stack) MarshalJSON() ([]byte, error) {
return json.Marshal(stackToArray(s))
}