neoneo-go/pkg/vm/stack/stack.go

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package stack
import (
"errors"
"fmt"
)
const (
// StackAverageSize is used to set the capacity of the stack
// setting this number too low, will cause extra allocations
StackAverageSize = 20
)
// RandomAccess represents a Random Access Stack
type RandomAccess struct {
vals []Item
}
// New will return a new random access stack
func New() *RandomAccess {
return &RandomAccess{
vals: make([]Item, 0, StackAverageSize),
}
}
// Items will return all items in the stack
func (ras *RandomAccess) items() []Item {
return ras.vals
}
//Len will return the length of the stack
func (ras *RandomAccess) Len() int {
if ras.vals == nil {
return -1
}
return len(ras.vals)
}
// Clear will remove all items in the stack
func (ras *RandomAccess) Clear() {
ras.vals = make([]Item, 0, StackAverageSize)
}
// Pop will remove the last stack item that was added
func (ras *RandomAccess) Pop() (Item, error) {
if len(ras.vals) == 0 {
return nil, errors.New("There are no items on the stack to pop")
}
if ras.vals == nil {
return nil, errors.New("Cannot pop from a nil stack")
}
l := len(ras.vals)
item := ras.vals[l-1]
ras.vals = ras.vals[:l-1]
return item, nil
}
// Push will put a stack item onto the top of the stack
func (ras *RandomAccess) Push(item Item) *RandomAccess {
if ras.vals == nil {
ras.vals = make([]Item, 0, StackAverageSize)
}
ras.vals = append(ras.vals, item)
return ras
}
// Insert will push a stackItem onto the stack at position `n`
// Note; index 0 is the top of the stack, which is the end of slice
func (ras *RandomAccess) Insert(n uint16, item Item) (*RandomAccess, error) {
if n == 0 {
return ras.Push(item), nil
}
if ras.vals == nil {
ras.vals = make([]Item, 0, StackAverageSize)
}
// Check that we are not inserting out of the bounds
stackSize := uint16(len(ras.vals))
if n > stackSize-1 {
return nil, fmt.Errorf("Tried to insert at index %d when length of stack is %d", n, len(ras.vals))
}
index := stackSize - n
ras.vals = append(ras.vals, item)
copy(ras.vals[index:], ras.vals[index-1:])
ras.vals[index] = item
return ras, nil
}
// Peek will check an element at a given index
// Note: 0 is the top of the stack, which is the end of the slice
func (ras *RandomAccess) Peek(n uint16) (Item, error) {
stackSize := uint16(len(ras.vals))
if n == 0 {
index := stackSize - 1
return ras.vals[index], nil
}
if ras.vals == nil {
return nil, errors.New("Cannot peak at a nil stack")
}
// Check that we are not peeking out of the bounds
if n > stackSize-1 {
return nil, fmt.Errorf("Tried to peek at index %d when length of stack is %d", n, len(ras.vals))
}
index := stackSize - n - 1
return ras.vals[index], nil
}