neoneo-go/pkg/vm/stack.go

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package vm
import (
"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
}
// 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
default:
b := t.Value().([]uint8)
return new(big.Int).SetBytes(util.ArrayReverse(b))
}
}
// 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 {
if v, ok := e.value.Value().(*big.Int); ok {
return v.Int64() == 1
}
return e.value.Value().(bool)
}
// 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 {
return e.value.Value().([]byte)
}
// Stack represents a Stack backed by a double linked list.
type Stack struct {
top Element
name string
len 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
return s
}
// Clear will clear 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
}
// Len return the number of elements that are on the stack.
func (s *Stack) Len() int {
return s.len
}
// insert will insert 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++
return e
}
// InsertBefore will insert the element before the mark on the stack.
func (s *Stack) InsertBefore(e, mark *Element) *Element {
if mark == nil {
return nil
}
return s.insert(e, mark.prev)
}
// InsertAt will insert the given item (n) deep on the stack.
func (s *Stack) InsertAt(e *Element, n int) *Element {
before := s.Peek(n)
if before == nil {
return nil
}
return s.InsertBefore(e, before)
}
// Push pushes the given element on the stack.
func (s *Stack) Push(e *Element) {
s.insert(e, &s.top)
}
// PushVal will push 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--
return e
}
// Dup will duplicate and return 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,
}
}
// Iter will iterate 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)
}
}