core, tests: reduced state copy by N calls

Reduced the amount of state copied that are required by N calls by doing
a balance check prior to any state modifications.

core/vm/environment.go

@@ -36,6 +36,7 @@ type Environment interface {
 	Time() uint64
 	Difficulty() *big.Int
 	GasLimit() *big.Int
+	CanTransfer(from Account, balance *big.Int) bool
 	Transfer(from, to Account, amount *big.Int) error
 	AddLog(*state.Log)
 	AddStructLog(StructLog)

core/vm/instructions.go

@@ -13,6 +13,7 @@
 //
 // You should have received a copy of the GNU Lesser General Public License
 // along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
 package vm
 
 import (

core/vm/jit.go

@@ -13,6 +13,7 @@
 //
 // You should have received a copy of the GNU Lesser General Public License
 // along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
 package vm
 
 import (
@@ -48,7 +49,7 @@ func SetJITCacheSize(size int) {
 	programs, _ = lru.New(size)
 }
 
-// GetProgram returns the program by id or nil when non-existant
+// GetProgram returns the program by id or nil when non-existent
 func GetProgram(id common.Hash) *Program {
 	if p, ok := programs.Get(id); ok {
 		return p.(*Program)

core/vm/jit_test.go

@@ -105,6 +105,9 @@ func (self *Env) AddLog(log *state.Log) {
 }
 func (self *Env) Depth() int     { return self.depth }
 func (self *Env) SetDepth(i int) { self.depth = i }
+func (self *Env) CanTransfer(from Account, balance *big.Int) bool {
+	return from.Balance().Cmp(balance) >= 0
+}
 func (self *Env) Transfer(from, to Account, amount *big.Int) error {
 	return nil
 }

core/vm/settings.go

@@ -13,6 +13,7 @@
 //
 // You should have received a copy of the GNU Lesser General Public License
 // along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
 package vm
 
 var (