bsc/core/vm/vm.go

// Copyright 2014 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// 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 implements the Ethereum Virtual Machine.
package vm

import (
	"fmt"
	"math/big"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/core/state"
	"github.com/ethereum/go-ethereum/crypto"
	"github.com/ethereum/go-ethereum/logger"
	"github.com/ethereum/go-ethereum/logger/glog"
	"github.com/ethereum/go-ethereum/params"
)

// Vm implements VirtualMachine
type Vm struct {
	env Environment
}

// New returns a new Virtual Machine
func New(env Environment) *Vm {
	return &Vm{env: env}
}

// Run loops and evaluates the contract's code with the given input data
func (self *Vm) Run(context *Context, input []byte) (ret []byte, err error) {
	self.env.SetDepth(self.env.Depth() + 1)
	defer self.env.SetDepth(self.env.Depth() - 1)

	// User defer pattern to check for an error and, based on the error being nil or not, use all gas and return.
	defer func() {
		if err != nil {
			// In case of a VM exception (known exceptions) all gas consumed (panics NOT included).
			context.UseGas(context.Gas)

			ret = context.Return(nil)
		}
	}()

	if context.CodeAddr != nil {
		if p := Precompiled[context.CodeAddr.Str()]; p != nil {
			return self.RunPrecompiled(p, input, context)
		}
	}

	var (
		codehash = crypto.Sha3Hash(context.Code) // codehash is used when doing jump dest caching
		program  *Program
	)
	if EnableJit {
		// Fetch program status.
		// * If ready run using JIT
		// * If unknown, compile in a seperate goroutine
		// * If forced wait for compilation and run once done
		if status := GetProgramStatus(codehash); status == progReady {
			return RunProgram(GetProgram(codehash), self.env, context, input)
		} else if status == progUnknown {
			if ForceJit {
				// Create and compile program
				program = NewProgram(context.Code)
				perr := CompileProgram(program)
				if perr == nil {
					return RunProgram(program, self.env, context, input)
				}
				glog.V(logger.Info).Infoln("error compiling program", err)
			} else {
				// create and compile the program. Compilation
				// is done in a seperate goroutine
				program = NewProgram(context.Code)
				go func() {
					err := CompileProgram(program)
					if err != nil {
						glog.V(logger.Info).Infoln("error compiling program", err)
						return
					}
				}()
			}
		}
	}

	var (
		caller = context.caller
		code   = context.Code
		value  = context.value
		price  = context.Price

		op      OpCode             // current opcode
		mem     = NewMemory()      // bound memory
		stack   = newstack()       // local stack
		statedb = self.env.State() // current state
		// For optimisation reason we're using uint64 as the program counter.
		// It's theoretically possible to go above 2^64. The YP defines the PC to be uint256. Pratically much less so feasible.
		pc = uint64(0) // program counter

		// jump evaluates and checks whether the given jump destination is a valid one
		// if valid move the `pc` otherwise return an error.
		jump = func(from uint64, to *big.Int) error {
			if !context.jumpdests.has(codehash, code, to) {
				nop := context.GetOp(to.Uint64())
				return fmt.Errorf("invalid jump destination (%v) %v", nop, to)
			}

			pc = to.Uint64()

			return nil
		}

		newMemSize *big.Int
		cost       *big.Int
	)

	// User defer pattern to check for an error and, based on the error being nil or not, use all gas and return.
	defer func() {
		if err != nil {
			self.log(pc, op, context.Gas, cost, mem, stack, context, err)
		}
	}()

	// Don't bother with the execution if there's no code.
	if len(code) == 0 {
		return context.Return(nil), nil
	}

	for {
		// Overhead of the atomic read might not be worth it
		/* TODO this still causes a few issues in the tests
		if program != nil && progStatus(atomic.LoadInt32(&program.status)) == progReady {
			// move execution
			glog.V(logger.Info).Infoln("Moved execution to JIT")
			return runProgram(program, pc, mem, stack, self.env, context, input)
		}
		*/
		// The base for all big integer arithmetic
		base := new(big.Int)

		// Get the memory location of pc
		op = context.GetOp(pc)

		// calculate the new memory size and gas price for the current executing opcode
		newMemSize, cost, err = calculateGasAndSize(self.env, context, caller, op, statedb, mem, stack)
		if err != nil {
			return nil, err
		}

		// Use the calculated gas. When insufficient gas is present, use all gas and return an
		// Out Of Gas error
		if !context.UseGas(cost) {
			return nil, OutOfGasError
		}

		// Resize the memory calculated previously
		mem.Resize(newMemSize.Uint64())
		// Add a log message
		self.log(pc, op, context.Gas, cost, mem, stack, context, nil)

		switch op {
		case ADD:
			x, y := stack.pop(), stack.pop()

			base.Add(x, y)

			U256(base)

			// pop result back on the stack
			stack.push(base)
		case SUB:
			x, y := stack.pop(), stack.pop()

			base.Sub(x, y)

			U256(base)

			// pop result back on the stack
			stack.push(base)
		case MUL:
			x, y := stack.pop(), stack.pop()

			base.Mul(x, y)

			U256(base)

			// pop result back on the stack
			stack.push(base)
		case DIV:
			x, y := stack.pop(), stack.pop()

			if y.Cmp(common.Big0) != 0 {
				base.Div(x, y)
			}

			U256(base)

			// pop result back on the stack
			stack.push(base)
		case SDIV:
			x, y := S256(stack.pop()), S256(stack.pop())

			if y.Cmp(common.Big0) == 0 {
				base.Set(common.Big0)
			} else {
				n := new(big.Int)
				if new(big.Int).Mul(x, y).Cmp(common.Big0) < 0 {
					n.SetInt64(-1)
				} else {
					n.SetInt64(1)
				}

				base.Div(x.Abs(x), y.Abs(y)).Mul(base, n)

				U256(base)
			}

			stack.push(base)
		case MOD:
			x, y := stack.pop(), stack.pop()

			if y.Cmp(common.Big0) == 0 {
				base.Set(common.Big0)
			} else {
				base.Mod(x, y)
			}

			U256(base)

			stack.push(base)
		case SMOD:
			x, y := S256(stack.pop()), S256(stack.pop())

			if y.Cmp(common.Big0) == 0 {
				base.Set(common.Big0)
			} else {
				n := new(big.Int)
				if x.Cmp(common.Big0) < 0 {
					n.SetInt64(-1)
				} else {
					n.SetInt64(1)
				}

				base.Mod(x.Abs(x), y.Abs(y)).Mul(base, n)

				U256(base)
			}

			stack.push(base)

		case EXP:
			x, y := stack.pop(), stack.pop()

			base.Exp(x, y, Pow256)

			U256(base)

			stack.push(base)
		case SIGNEXTEND:
			back := stack.pop()
			if back.Cmp(big.NewInt(31)) < 0 {
				bit := uint(back.Uint64()*8 + 7)
				num := stack.pop()
				mask := new(big.Int).Lsh(common.Big1, bit)
				mask.Sub(mask, common.Big1)
				if common.BitTest(num, int(bit)) {
					num.Or(num, mask.Not(mask))
				} else {
					num.And(num, mask)
				}

				num = U256(num)

				stack.push(num)
			}
		case NOT:
			stack.push(U256(new(big.Int).Not(stack.pop())))
		case LT:
			x, y := stack.pop(), stack.pop()

			// x < y
			if x.Cmp(y) < 0 {
				stack.push(common.BigTrue)
			} else {
				stack.push(common.BigFalse)
			}
		case GT:
			x, y := stack.pop(), stack.pop()

			// x > y
			if x.Cmp(y) > 0 {
				stack.push(common.BigTrue)
			} else {
				stack.push(common.BigFalse)
			}

		case SLT:
			x, y := S256(stack.pop()), S256(stack.pop())

			// x < y
			if x.Cmp(S256(y)) < 0 {
				stack.push(common.BigTrue)
			} else {
				stack.push(common.BigFalse)
			}
		case SGT:
			x, y := S256(stack.pop()), S256(stack.pop())

			// x > y
			if x.Cmp(y) > 0 {
				stack.push(common.BigTrue)
			} else {
				stack.push(common.BigFalse)
			}

		case EQ:
			x, y := stack.pop(), stack.pop()

			// x == y
			if x.Cmp(y) == 0 {
				stack.push(common.BigTrue)
			} else {
				stack.push(common.BigFalse)
			}
		case ISZERO:
			x := stack.pop()
			if x.Cmp(common.BigFalse) > 0 {
				stack.push(common.BigFalse)
			} else {
				stack.push(common.BigTrue)
			}

		case AND:
			x, y := stack.pop(), stack.pop()

			stack.push(base.And(x, y))
		case OR:
			x, y := stack.pop(), stack.pop()

			stack.push(base.Or(x, y))
		case XOR:
			x, y := stack.pop(), stack.pop()

			stack.push(base.Xor(x, y))
		case BYTE:
			th, val := stack.pop(), stack.pop()

			if th.Cmp(big.NewInt(32)) < 0 {
				byt := big.NewInt(int64(common.LeftPadBytes(val.Bytes(), 32)[th.Int64()]))

				base.Set(byt)
			} else {
				base.Set(common.BigFalse)
			}

			stack.push(base)
		case ADDMOD:
			x := stack.pop()
			y := stack.pop()
			z := stack.pop()

			if z.Cmp(Zero) > 0 {
				add := new(big.Int).Add(x, y)
				base.Mod(add, z)

				base = U256(base)
			}

			stack.push(base)
		case MULMOD:
			x := stack.pop()
			y := stack.pop()
			z := stack.pop()

			if z.Cmp(Zero) > 0 {
				mul := new(big.Int).Mul(x, y)
				base.Mod(mul, z)

				U256(base)
			}

			stack.push(base)

		case SHA3:
			offset, size := stack.pop(), stack.pop()
			data := crypto.Sha3(mem.Get(offset.Int64(), size.Int64()))

			stack.push(common.BigD(data))

		case ADDRESS:
			stack.push(common.Bytes2Big(context.Address().Bytes()))

		case BALANCE:
			addr := common.BigToAddress(stack.pop())
			balance := statedb.GetBalance(addr)

			stack.push(new(big.Int).Set(balance))

		case ORIGIN:
			origin := self.env.Origin()

			stack.push(origin.Big())

		case CALLER:
			caller := context.caller.Address()
			stack.push(common.Bytes2Big(caller.Bytes()))

		case CALLVALUE:
			stack.push(new(big.Int).Set(value))

		case CALLDATALOAD:
			data := getData(input, stack.pop(), common.Big32)

			stack.push(common.Bytes2Big(data))
		case CALLDATASIZE:
			l := int64(len(input))
			stack.push(big.NewInt(l))

		case CALLDATACOPY:
			var (
				mOff = stack.pop()
				cOff = stack.pop()
				l    = stack.pop()
			)
			data := getData(input, cOff, l)

			mem.Set(mOff.Uint64(), l.Uint64(), data)

		case CODESIZE, EXTCODESIZE:
			var code []byte
			if op == EXTCODESIZE {
				addr := common.BigToAddress(stack.pop())

				code = statedb.GetCode(addr)
			} else {
				code = context.Code
			}

			l := big.NewInt(int64(len(code)))
			stack.push(l)

		case CODECOPY, EXTCODECOPY:
			var code []byte
			if op == EXTCODECOPY {
				addr := common.BigToAddress(stack.pop())
				code = statedb.GetCode(addr)
			} else {
				code = context.Code
			}

			var (
				mOff = stack.pop()
				cOff = stack.pop()
				l    = stack.pop()
			)

			codeCopy := getData(code, cOff, l)

			mem.Set(mOff.Uint64(), l.Uint64(), codeCopy)

		case GASPRICE:
			stack.push(new(big.Int).Set(context.Price))

		case BLOCKHASH:
			num := stack.pop()

			n := new(big.Int).Sub(self.env.BlockNumber(), common.Big257)
			if num.Cmp(n) > 0 && num.Cmp(self.env.BlockNumber()) < 0 {
				stack.push(self.env.GetHash(num.Uint64()).Big())
			} else {
				stack.push(common.Big0)
			}

		case COINBASE:
			coinbase := self.env.Coinbase()

			stack.push(coinbase.Big())

		case TIMESTAMP:
			time := self.env.Time()

			stack.push(new(big.Int).Set(time))

		case NUMBER:
			number := self.env.BlockNumber()

			stack.push(U256(number))

		case DIFFICULTY:
			difficulty := self.env.Difficulty()

			stack.push(new(big.Int).Set(difficulty))

		case GASLIMIT:

			stack.push(new(big.Int).Set(self.env.GasLimit()))

		case PUSH1, PUSH2, PUSH3, PUSH4, PUSH5, PUSH6, PUSH7, PUSH8, PUSH9, PUSH10, PUSH11, PUSH12, PUSH13, PUSH14, PUSH15, PUSH16, PUSH17, PUSH18, PUSH19, PUSH20, PUSH21, PUSH22, PUSH23, PUSH24, PUSH25, PUSH26, PUSH27, PUSH28, PUSH29, PUSH30, PUSH31, PUSH32:
			size := uint64(op - PUSH1 + 1)
			byts := getData(code, new(big.Int).SetUint64(pc+1), new(big.Int).SetUint64(size))
			// push value to stack
			stack.push(common.Bytes2Big(byts))
			pc += size

		case POP:
			stack.pop()
		case DUP1, DUP2, DUP3, DUP4, DUP5, DUP6, DUP7, DUP8, DUP9, DUP10, DUP11, DUP12, DUP13, DUP14, DUP15, DUP16:
			n := int(op - DUP1 + 1)
			stack.dup(n)

		case SWAP1, SWAP2, SWAP3, SWAP4, SWAP5, SWAP6, SWAP7, SWAP8, SWAP9, SWAP10, SWAP11, SWAP12, SWAP13, SWAP14, SWAP15, SWAP16:
			n := int(op - SWAP1 + 2)
			stack.swap(n)

		case LOG0, LOG1, LOG2, LOG3, LOG4:
			n := int(op - LOG0)
			topics := make([]common.Hash, n)
			mStart, mSize := stack.pop(), stack.pop()
			for i := 0; i < n; i++ {
				topics[i] = common.BigToHash(stack.pop())
			}

			data := mem.Get(mStart.Int64(), mSize.Int64())
			log := state.NewLog(context.Address(), topics, data, self.env.BlockNumber().Uint64())
			self.env.AddLog(log)

		case MLOAD:
			offset := stack.pop()
			val := common.BigD(mem.Get(offset.Int64(), 32))
			stack.push(val)

		case MSTORE:
			// pop value of the stack
			mStart, val := stack.pop(), stack.pop()
			mem.Set(mStart.Uint64(), 32, common.BigToBytes(val, 256))

		case MSTORE8:
			off, val := stack.pop().Int64(), stack.pop().Int64()

			mem.store[off] = byte(val & 0xff)

		case SLOAD:
			loc := common.BigToHash(stack.pop())
			val := statedb.GetState(context.Address(), loc).Big()
			stack.push(val)

		case SSTORE:
			loc := common.BigToHash(stack.pop())
			val := stack.pop()

			statedb.SetState(context.Address(), loc, common.BigToHash(val))

		case JUMP:
			if err := jump(pc, stack.pop()); err != nil {
				return nil, err
			}

			continue
		case JUMPI:
			pos, cond := stack.pop(), stack.pop()

			if cond.Cmp(common.BigTrue) >= 0 {
				if err := jump(pc, pos); err != nil {
					return nil, err
				}

				continue
			}

		case JUMPDEST:
		case PC:
			stack.push(new(big.Int).SetUint64(pc))
		case MSIZE:
			stack.push(big.NewInt(int64(mem.Len())))
		case GAS:
			stack.push(new(big.Int).Set(context.Gas))
		case CREATE:

			var (
				value        = stack.pop()
				offset, size = stack.pop(), stack.pop()
				input        = mem.Get(offset.Int64(), size.Int64())
				gas          = new(big.Int).Set(context.Gas)
				addr         common.Address
			)

			context.UseGas(context.Gas)
			ret, suberr, ref := self.env.Create(context, input, gas, price, value)
			if suberr != nil {
				stack.push(common.BigFalse)

			} else {
				// gas < len(ret) * CreateDataGas == NO_CODE
				dataGas := big.NewInt(int64(len(ret)))
				dataGas.Mul(dataGas, params.CreateDataGas)
				if context.UseGas(dataGas) {
					ref.SetCode(ret)
				}
				addr = ref.Address()

				stack.push(addr.Big())

			}

		case CALL, CALLCODE:
			gas := stack.pop()
			// pop gas and value of the stack.
			addr, value := stack.pop(), stack.pop()
			value = U256(value)
			// pop input size and offset
			inOffset, inSize := stack.pop(), stack.pop()
			// pop return size and offset
			retOffset, retSize := stack.pop(), stack.pop()

			address := common.BigToAddress(addr)

			// Get the arguments from the memory
			args := mem.Get(inOffset.Int64(), inSize.Int64())

			if len(value.Bytes()) > 0 {
				gas.Add(gas, params.CallStipend)
			}

			var (
				ret []byte
				err error
			)
			if op == CALLCODE {
				ret, err = self.env.CallCode(context, address, args, gas, price, value)
			} else {
				ret, err = self.env.Call(context, address, args, gas, price, value)
			}

			if err != nil {
				stack.push(common.BigFalse)

			} else {
				stack.push(common.BigTrue)

				mem.Set(retOffset.Uint64(), retSize.Uint64(), ret)
			}

		case RETURN:
			offset, size := stack.pop(), stack.pop()
			ret := mem.GetPtr(offset.Int64(), size.Int64())

			return context.Return(ret), nil
		case SUICIDE:
			receiver := statedb.GetOrNewStateObject(common.BigToAddress(stack.pop()))
			balance := statedb.GetBalance(context.Address())

			receiver.AddBalance(balance)

			statedb.Delete(context.Address())

			fallthrough
		case STOP: // Stop the context

			return context.Return(nil), nil
		default:

			return nil, fmt.Errorf("Invalid opcode %x", op)
		}

		pc++

	}
}

// calculateGasAndSize calculates the required given the opcode and stack items calculates the new memorysize for
// the operation. This does not reduce gas or resizes the memory.
func calculateGasAndSize(env Environment, context *Context, caller ContextRef, op OpCode, statedb *state.StateDB, mem *Memory, stack *stack) (*big.Int, *big.Int, error) {
	var (
		gas                 = new(big.Int)
		newMemSize *big.Int = new(big.Int)
	)
	err := baseCheck(op, stack, gas)
	if err != nil {
		return nil, nil, err
	}

	// stack Check, memory resize & gas phase
	switch op {
	case SWAP1, SWAP2, SWAP3, SWAP4, SWAP5, SWAP6, SWAP7, SWAP8, SWAP9, SWAP10, SWAP11, SWAP12, SWAP13, SWAP14, SWAP15, SWAP16:
		n := int(op - SWAP1 + 2)
		err := stack.require(n)
		if err != nil {
			return nil, nil, err
		}
		gas.Set(GasFastestStep)
	case DUP1, DUP2, DUP3, DUP4, DUP5, DUP6, DUP7, DUP8, DUP9, DUP10, DUP11, DUP12, DUP13, DUP14, DUP15, DUP16:
		n := int(op - DUP1 + 1)
		err := stack.require(n)
		if err != nil {
			return nil, nil, err
		}
		gas.Set(GasFastestStep)
	case LOG0, LOG1, LOG2, LOG3, LOG4:
		n := int(op - LOG0)
		err := stack.require(n + 2)
		if err != nil {
			return nil, nil, err
		}

		mSize, mStart := stack.data[stack.len()-2], stack.data[stack.len()-1]

		gas.Add(gas, params.LogGas)
		gas.Add(gas, new(big.Int).Mul(big.NewInt(int64(n)), params.LogTopicGas))
		gas.Add(gas, new(big.Int).Mul(mSize, params.LogDataGas))

		newMemSize = calcMemSize(mStart, mSize)
	case EXP:
		gas.Add(gas, new(big.Int).Mul(big.NewInt(int64(len(stack.data[stack.len()-2].Bytes()))), params.ExpByteGas))
	case SSTORE:
		err := stack.require(2)
		if err != nil {
			return nil, nil, err
		}

		var g *big.Int
		y, x := stack.data[stack.len()-2], stack.data[stack.len()-1]
		val := statedb.GetState(context.Address(), common.BigToHash(x))

		// This checks for 3 scenario's and calculates gas accordingly
		// 1. From a zero-value address to a non-zero value         (NEW VALUE)
		// 2. From a non-zero value address to a zero-value address (DELETE)
		// 3. From a nen-zero to a non-zero                         (CHANGE)
		if common.EmptyHash(val) && !common.EmptyHash(common.BigToHash(y)) {
			// 0 => non 0
			g = params.SstoreSetGas
		} else if !common.EmptyHash(val) && common.EmptyHash(common.BigToHash(y)) {
			statedb.Refund(params.SstoreRefundGas)

			g = params.SstoreClearGas
		} else {
			// non 0 => non 0 (or 0 => 0)
			g = params.SstoreClearGas
		}
		gas.Set(g)
	case SUICIDE:
		if !statedb.IsDeleted(context.Address()) {
			statedb.Refund(params.SuicideRefundGas)
		}
	case MLOAD:
		newMemSize = calcMemSize(stack.peek(), u256(32))
	case MSTORE8:
		newMemSize = calcMemSize(stack.peek(), u256(1))
	case MSTORE:
		newMemSize = calcMemSize(stack.peek(), u256(32))
	case RETURN:
		newMemSize = calcMemSize(stack.peek(), stack.data[stack.len()-2])
	case SHA3:
		newMemSize = calcMemSize(stack.peek(), stack.data[stack.len()-2])

		words := toWordSize(stack.data[stack.len()-2])
		gas.Add(gas, words.Mul(words, params.Sha3WordGas))
	case CALLDATACOPY:
		newMemSize = calcMemSize(stack.peek(), stack.data[stack.len()-3])

		words := toWordSize(stack.data[stack.len()-3])
		gas.Add(gas, words.Mul(words, params.CopyGas))
	case CODECOPY:
		newMemSize = calcMemSize(stack.peek(), stack.data[stack.len()-3])

		words := toWordSize(stack.data[stack.len()-3])
		gas.Add(gas, words.Mul(words, params.CopyGas))
	case EXTCODECOPY:
		newMemSize = calcMemSize(stack.data[stack.len()-2], stack.data[stack.len()-4])

		words := toWordSize(stack.data[stack.len()-4])
		gas.Add(gas, words.Mul(words, params.CopyGas))

	case CREATE:
		newMemSize = calcMemSize(stack.data[stack.len()-2], stack.data[stack.len()-3])
	case CALL, CALLCODE:
		gas.Add(gas, stack.data[stack.len()-1])

		if op == CALL {
			if env.State().GetStateObject(common.BigToAddress(stack.data[stack.len()-2])) == nil {
				gas.Add(gas, params.CallNewAccountGas)
			}
		}

		if len(stack.data[stack.len()-3].Bytes()) > 0 {
			gas.Add(gas, params.CallValueTransferGas)
		}

		x := calcMemSize(stack.data[stack.len()-6], stack.data[stack.len()-7])
		y := calcMemSize(stack.data[stack.len()-4], stack.data[stack.len()-5])

		newMemSize = common.BigMax(x, y)
	}

	if newMemSize.Cmp(common.Big0) > 0 {
		newMemSizeWords := toWordSize(newMemSize)
		newMemSize.Mul(newMemSizeWords, u256(32))

		if newMemSize.Cmp(u256(int64(mem.Len()))) > 0 {
			oldSize := toWordSize(big.NewInt(int64(mem.Len())))
			pow := new(big.Int).Exp(oldSize, common.Big2, Zero)
			linCoef := new(big.Int).Mul(oldSize, params.MemoryGas)
			quadCoef := new(big.Int).Div(pow, params.QuadCoeffDiv)
			oldTotalFee := new(big.Int).Add(linCoef, quadCoef)

			pow.Exp(newMemSizeWords, common.Big2, Zero)
			linCoef = new(big.Int).Mul(newMemSizeWords, params.MemoryGas)
			quadCoef = new(big.Int).Div(pow, params.QuadCoeffDiv)
			newTotalFee := new(big.Int).Add(linCoef, quadCoef)

			fee := new(big.Int).Sub(newTotalFee, oldTotalFee)
			gas.Add(gas, fee)
		}
	}

	return newMemSize, gas, nil
}

// RunPrecompile runs and evaluate the output of a precompiled contract defined in contracts.go
func (self *Vm) RunPrecompiled(p *PrecompiledAccount, input []byte, context *Context) (ret []byte, err error) {
	gas := p.Gas(len(input))
	if context.UseGas(gas) {
		ret = p.Call(input)

		return context.Return(ret), nil
	} else {
		return nil, OutOfGasError
	}
}

// log emits a log event to the environment for each opcode encountered. This is not to be confused with the
// LOG* opcode.
func (self *Vm) log(pc uint64, op OpCode, gas, cost *big.Int, memory *Memory, stack *stack, context *Context, err error) {
	if Debug {
		mem := make([]byte, len(memory.Data()))
		copy(mem, memory.Data())
		stck := make([]*big.Int, len(stack.Data()))
		copy(stck, stack.Data())

		object := context.self.(*state.StateObject)
		storage := make(map[common.Hash][]byte)
		object.EachStorage(func(k, v []byte) {
			storage[common.BytesToHash(k)] = v
		})

		self.env.AddStructLog(StructLog{pc, op, new(big.Int).Set(gas), cost, mem, stck, storage, err})
	}
}

// Environment returns the current workable state of the VM
func (self *Vm) Env() Environment {
	return self.env
}