From 78745551c077bf54151202138c2629f288769561 Mon Sep 17 00:00:00 2001
From: Determinant <tederminant@gmail.com>
Date: Tue, 15 Sep 2020 23:55:34 -0400
Subject: WIP: geth-tavum

---
 core/vm/stack.go | 84 ++++++++++++++++++++++++++++++++++++++++----------------
 1 file changed, 60 insertions(+), 24 deletions(-)

(limited to 'core/vm/stack.go')

diff --git a/core/vm/stack.go b/core/vm/stack.go
index 4c1b9e8..af27d65 100644
--- a/core/vm/stack.go
+++ b/core/vm/stack.go
@@ -18,36 +18,48 @@ package vm
 
 import (
 	"fmt"
-	"math/big"
+	"sync"
+
+	"github.com/holiman/uint256"
 )
 
+var stackPool = sync.Pool{
+	New: func() interface{} {
+		return &Stack{data: make([]uint256.Int, 0, 16)}
+	},
+}
+
 // Stack is an object for basic stack operations. Items popped to the stack are
 // expected to be changed and modified. stack does not take care of adding newly
 // initialised objects.
 type Stack struct {
-	data []*big.Int
+	data []uint256.Int
 }
 
 func newstack() *Stack {
-	return &Stack{data: make([]*big.Int, 0, 1024)}
+	return stackPool.Get().(*Stack)
 }
 
-// Data returns the underlying big.Int array.
-func (st *Stack) Data() []*big.Int {
+func returnStack(s *Stack) {
+	s.data = s.data[:0]
+	stackPool.Put(s)
+}
+
+// Data returns the underlying uint256.Int array.
+func (st *Stack) Data() []uint256.Int {
 	return st.data
 }
 
-func (st *Stack) push(d *big.Int) {
+func (st *Stack) push(d *uint256.Int) {
 	// NOTE push limit (1024) is checked in baseCheck
-	//stackItem := new(big.Int).Set(d)
-	//st.data = append(st.data, stackItem)
-	st.data = append(st.data, d)
+	st.data = append(st.data, *d)
 }
-func (st *Stack) pushN(ds ...*big.Int) {
+func (st *Stack) pushN(ds ...uint256.Int) {
+	// FIXME: Is there a way to pass args by pointers.
 	st.data = append(st.data, ds...)
 }
 
-func (st *Stack) pop() (ret *big.Int) {
+func (st *Stack) pop() (ret uint256.Int) {
 	ret = st.data[len(st.data)-1]
 	st.data = st.data[:len(st.data)-1]
 	return
@@ -61,24 +73,17 @@ func (st *Stack) swap(n int) {
 	st.data[st.len()-n], st.data[st.len()-1] = st.data[st.len()-1], st.data[st.len()-n]
 }
 
-func (st *Stack) dup(pool *intPool, n int) {
-	st.push(pool.get().Set(st.data[st.len()-n]))
+func (st *Stack) dup(n int) {
+	st.push(&st.data[st.len()-n])
 }
 
-func (st *Stack) peek() *big.Int {
-	return st.data[st.len()-1]
+func (st *Stack) peek() *uint256.Int {
+	return &st.data[st.len()-1]
 }
 
 // Back returns the n'th item in stack
-func (st *Stack) Back(n int) *big.Int {
-	return st.data[st.len()-n-1]
-}
-
-func (st *Stack) require(n int) error {
-	if st.len() < n {
-		return fmt.Errorf("stack underflow (%d <=> %d)", len(st.data), n)
-	}
-	return nil
+func (st *Stack) Back(n int) *uint256.Int {
+	return &st.data[st.len()-n-1]
 }
 
 // Print dumps the content of the stack
@@ -93,3 +98,34 @@ func (st *Stack) Print() {
 	}
 	fmt.Println("#############")
 }
+
+var rStackPool = sync.Pool{
+	New: func() interface{} {
+		return &ReturnStack{data: make([]uint32, 0, 10)}
+	},
+}
+
+// ReturnStack is an object for basic return stack operations.
+type ReturnStack struct {
+	data []uint32
+}
+
+func newReturnStack() *ReturnStack {
+	return rStackPool.Get().(*ReturnStack)
+}
+
+func returnRStack(rs *ReturnStack) {
+	rs.data = rs.data[:0]
+	rStackPool.Put(rs)
+}
+
+func (st *ReturnStack) push(d uint32) {
+	st.data = append(st.data, d)
+}
+
+// A uint32 is sufficient as for code below 4.2G
+func (st *ReturnStack) pop() (ret uint32) {
+	ret = st.data[len(st.data)-1]
+	st.data = st.data[:len(st.data)-1]
+	return
+}
-- 
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