362 lines
8.6 KiB
Go
362 lines
8.6 KiB
Go
// Copyright (c) 2013-2017 The btcsuite developers
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// Use of this source code is governed by an ISC
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// license that can be found in the LICENSE file.
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package txscript
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import (
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"encoding/hex"
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"fmt"
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)
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// asBool gets the boolean value of the byte array.
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func asBool(t []byte) bool {
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for i := range t {
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if t[i] != 0 {
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// Negative 0 is also considered false.
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if i == len(t)-1 && t[i] == 0x80 {
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return false
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}
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return true
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}
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}
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return false
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}
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// fromBool converts a boolean into the appropriate byte array.
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func fromBool(v bool) []byte {
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if v {
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return []byte{1}
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}
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return nil
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}
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// stack represents a stack of immutable objects to be used with bitcoin
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// scripts. Objects may be shared, therefore in usage if a value is to be
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// changed it *must* be deep-copied first to avoid changing other values on the
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// stack.
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type stack struct {
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stk [][]byte
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verifyMinimalData bool
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}
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// Depth returns the number of items on the stack.
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func (s *stack) Depth() int32 {
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return int32(len(s.stk))
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}
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// PushByteArray adds the given back array to the top of the stack.
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//
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// Stack transformation: [... x1 x2] -> [... x1 x2 data]
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func (s *stack) PushByteArray(so []byte) {
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s.stk = append(s.stk, so)
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}
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// PushInt converts the provided scriptNum to a suitable byte array then pushes
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// it onto the top of the stack.
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//
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// Stack transformation: [... x1 x2] -> [... x1 x2 int]
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func (s *stack) PushInt(val scriptNum) {
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s.PushByteArray(val.Bytes())
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}
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// PushBool converts the provided boolean to a suitable byte array then pushes
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// it onto the top of the stack.
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//
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// Stack transformation: [... x1 x2] -> [... x1 x2 bool]
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func (s *stack) PushBool(val bool) {
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s.PushByteArray(fromBool(val))
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}
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// PopByteArray pops the value off the top of the stack and returns it.
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//
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// Stack transformation: [... x1 x2 x3] -> [... x1 x2]
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func (s *stack) PopByteArray() ([]byte, error) {
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return s.nipN(0)
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}
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// PopInt pops the value off the top of the stack, converts it into a script
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// num, and returns it. The act of converting to a script num enforces the
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// consensus rules imposed on data interpreted as numbers.
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//
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// Stack transformation: [... x1 x2 x3] -> [... x1 x2]
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func (s *stack) PopInt() (scriptNum, error) {
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so, err := s.PopByteArray()
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if err != nil {
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return 0, err
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}
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return makeScriptNum(so, s.verifyMinimalData, maxScriptNumLen)
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}
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// PopBool pops the value off the top of the stack, converts it into a bool, and
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// returns it.
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//
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// Stack transformation: [... x1 x2 x3] -> [... x1 x2]
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func (s *stack) PopBool() (bool, error) {
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so, err := s.PopByteArray()
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if err != nil {
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return false, err
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}
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return asBool(so), nil
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}
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// PeekByteArray returns the Nth item on the stack without removing it.
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func (s *stack) PeekByteArray(idx int32) ([]byte, error) {
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sz := int32(len(s.stk))
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if idx < 0 || idx >= sz {
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str := fmt.Sprintf("index %d is invalid for stack size %d", idx,
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sz)
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return nil, scriptError(ErrInvalidStackOperation, str)
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}
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return s.stk[sz-idx-1], nil
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}
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// PeekInt returns the Nth item on the stack as a script num without removing
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// it. The act of converting to a script num enforces the consensus rules
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// imposed on data interpreted as numbers.
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func (s *stack) PeekInt(idx int32) (scriptNum, error) {
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so, err := s.PeekByteArray(idx)
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if err != nil {
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return 0, err
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}
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return makeScriptNum(so, s.verifyMinimalData, maxScriptNumLen)
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}
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// PeekBool returns the Nth item on the stack as a bool without removing it.
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func (s *stack) PeekBool(idx int32) (bool, error) {
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so, err := s.PeekByteArray(idx)
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if err != nil {
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return false, err
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}
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return asBool(so), nil
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}
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// nipN is an internal function that removes the nth item on the stack and
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// returns it.
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//
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// Stack transformation:
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// nipN(0): [... x1 x2 x3] -> [... x1 x2]
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// nipN(1): [... x1 x2 x3] -> [... x1 x3]
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// nipN(2): [... x1 x2 x3] -> [... x2 x3]
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func (s *stack) nipN(idx int32) ([]byte, error) {
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sz := int32(len(s.stk))
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if idx < 0 || idx > sz-1 {
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str := fmt.Sprintf("index %d is invalid for stack size %d", idx,
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sz)
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return nil, scriptError(ErrInvalidStackOperation, str)
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}
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so := s.stk[sz-idx-1]
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if idx == 0 {
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s.stk = s.stk[:sz-1]
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} else if idx == sz-1 {
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s1 := make([][]byte, sz-1)
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copy(s1, s.stk[1:])
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s.stk = s1
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} else {
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s1 := s.stk[sz-idx : sz]
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s.stk = s.stk[:sz-idx-1]
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s.stk = append(s.stk, s1...)
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}
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return so, nil
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}
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// NipN removes the Nth object on the stack
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//
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// Stack transformation:
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// NipN(0): [... x1 x2 x3] -> [... x1 x2]
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// NipN(1): [... x1 x2 x3] -> [... x1 x3]
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// NipN(2): [... x1 x2 x3] -> [... x2 x3]
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func (s *stack) NipN(idx int32) error {
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_, err := s.nipN(idx)
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return err
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}
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// Tuck copies the item at the top of the stack and inserts it before the 2nd
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// to top item.
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//
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// Stack transformation: [... x1 x2] -> [... x2 x1 x2]
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func (s *stack) Tuck() error {
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so2, err := s.PopByteArray()
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if err != nil {
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return err
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}
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so1, err := s.PopByteArray()
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if err != nil {
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return err
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}
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s.PushByteArray(so2) // stack [... x2]
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s.PushByteArray(so1) // stack [... x2 x1]
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s.PushByteArray(so2) // stack [... x2 x1 x2]
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return nil
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}
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// DropN removes the top N items from the stack.
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//
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// Stack transformation:
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// DropN(1): [... x1 x2] -> [... x1]
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// DropN(2): [... x1 x2] -> [...]
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func (s *stack) DropN(n int32) error {
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if n < 1 {
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str := fmt.Sprintf("attempt to drop %d items from stack", n)
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return scriptError(ErrInvalidStackOperation, str)
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}
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for ; n > 0; n-- {
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_, err := s.PopByteArray()
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if err != nil {
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return err
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}
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}
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return nil
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}
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// DupN duplicates the top N items on the stack.
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//
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// Stack transformation:
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// DupN(1): [... x1 x2] -> [... x1 x2 x2]
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// DupN(2): [... x1 x2] -> [... x1 x2 x1 x2]
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func (s *stack) DupN(n int32) error {
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if n < 1 {
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str := fmt.Sprintf("attempt to dup %d stack items", n)
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return scriptError(ErrInvalidStackOperation, str)
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}
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// Iteratively duplicate the value n-1 down the stack n times.
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// This leaves an in-order duplicate of the top n items on the stack.
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for i := n; i > 0; i-- {
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so, err := s.PeekByteArray(n - 1)
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if err != nil {
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return err
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}
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s.PushByteArray(so)
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}
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return nil
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}
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// RotN rotates the top 3N items on the stack to the left N times.
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//
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// Stack transformation:
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// RotN(1): [... x1 x2 x3] -> [... x2 x3 x1]
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// RotN(2): [... x1 x2 x3 x4 x5 x6] -> [... x3 x4 x5 x6 x1 x2]
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func (s *stack) RotN(n int32) error {
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if n < 1 {
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str := fmt.Sprintf("attempt to rotate %d stack items", n)
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return scriptError(ErrInvalidStackOperation, str)
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}
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// Nip the 3n-1th item from the stack to the top n times to rotate
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// them up to the head of the stack.
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entry := 3*n - 1
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for i := n; i > 0; i-- {
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so, err := s.nipN(entry)
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if err != nil {
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return err
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}
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s.PushByteArray(so)
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}
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return nil
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}
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// SwapN swaps the top N items on the stack with those below them.
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//
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// Stack transformation:
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// SwapN(1): [... x1 x2] -> [... x2 x1]
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// SwapN(2): [... x1 x2 x3 x4] -> [... x3 x4 x1 x2]
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func (s *stack) SwapN(n int32) error {
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if n < 1 {
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str := fmt.Sprintf("attempt to swap %d stack items", n)
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return scriptError(ErrInvalidStackOperation, str)
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}
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entry := 2*n - 1
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for i := n; i > 0; i-- {
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// Swap 2n-1th entry to top.
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so, err := s.nipN(entry)
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if err != nil {
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return err
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}
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s.PushByteArray(so)
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}
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return nil
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}
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// OverN copies N items N items back to the top of the stack.
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//
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// Stack transformation:
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// OverN(1): [... x1 x2 x3] -> [... x1 x2 x3 x2]
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// OverN(2): [... x1 x2 x3 x4] -> [... x1 x2 x3 x4 x1 x2]
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func (s *stack) OverN(n int32) error {
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if n < 1 {
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str := fmt.Sprintf("attempt to perform over on %d stack items",
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n)
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return scriptError(ErrInvalidStackOperation, str)
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}
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// Copy 2n-1th entry to top of the stack.
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entry := 2*n - 1
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for ; n > 0; n-- {
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so, err := s.PeekByteArray(entry)
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if err != nil {
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return err
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}
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s.PushByteArray(so)
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}
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return nil
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}
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// PickN copies the item N items back in the stack to the top.
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//
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// Stack transformation:
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// PickN(0): [x1 x2 x3] -> [x1 x2 x3 x3]
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// PickN(1): [x1 x2 x3] -> [x1 x2 x3 x2]
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// PickN(2): [x1 x2 x3] -> [x1 x2 x3 x1]
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func (s *stack) PickN(n int32) error {
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so, err := s.PeekByteArray(n)
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if err != nil {
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return err
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}
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s.PushByteArray(so)
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return nil
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}
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// RollN moves the item N items back in the stack to the top.
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//
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// Stack transformation:
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// RollN(0): [x1 x2 x3] -> [x1 x2 x3]
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// RollN(1): [x1 x2 x3] -> [x1 x3 x2]
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// RollN(2): [x1 x2 x3] -> [x2 x3 x1]
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func (s *stack) RollN(n int32) error {
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so, err := s.nipN(n)
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if err != nil {
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return err
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}
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s.PushByteArray(so)
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return nil
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}
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// String returns the stack in a readable format.
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func (s *stack) String() string {
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var result string
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for _, stack := range s.stk {
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if len(stack) == 0 {
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result += "00000000 <empty>\n"
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}
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result += hex.Dump(stack)
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}
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return result
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}
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