// CalcGasLimit computes the gas limit of the next block after parent.
// The result may be modified by the caller.
// This is miner strategy, not consensus protocol.
func CalcGasLimit(parent *types.Block) *big.Int {
// contrib = (parentGasUsed * 3 / 2) / 1024
contrib := new(big.Int).Mul(parent.GasUsed(), big.NewInt(3))
contrib = contrib.Div(contrib, big.NewInt(2))
contrib = contrib.Div(contrib, params.GasLimitBoundDivisor)
// decay = parentGasLimit / 1024 -1
decay := new(big.Int).Div(parent.GasLimit(), params.GasLimitBoundDivisor)
decay.Sub(decay, big.NewInt(1))
/*
strategy: gasLimit of block-to-mine is set based on parent's
gasUsed value. if parentGasUsed > parentGasLimit * (2/3) then we
increase it, otherwise lower it (or leave it unchanged if it's right
at that usage) the amount increased/decreased depends on how far away
from parentGasLimit * (2/3) parentGasUsed is.
*/
gl := new(big.Int).Sub(parent.GasLimit(), decay)
gl = gl.Add(gl, contrib)
gl.Set(common.BigMax(gl, params.MinGasLimit))
// however, if we're now below the target (GenesisGasLimit) we increase the
// limit as much as we can (parentGasLimit / 1024 -1)
if gl.Cmp(params.GenesisGasLimit) < 0 {
gl.Add(parent.GasLimit(), decay)
gl.Set(common.BigMin(gl, params.GenesisGasLimit))
}
return gl
}
// CalcDifficulty is the difficulty adjustment algorithm. It returns
// the difficulty that a new block b should have when created at time
// given the parent block's time and difficulty.
func CalcDifficulty(time, parentTime uint64, parentNumber, parentDiff *big.Int) *big.Int {
diff := new(big.Int)
adjust := new(big.Int).Div(parentDiff, params.DifficultyBoundDivisor)
bigTime := new(big.Int)
bigParentTime := new(big.Int)
bigTime.SetUint64(time)
bigParentTime.SetUint64(parentTime)
if bigTime.Sub(bigTime, bigParentTime).Cmp(params.DurationLimit) < 0 {
diff.Add(parentDiff, adjust)
} else {
diff.Sub(parentDiff, adjust)
}
if diff.Cmp(params.MinimumDifficulty) < 0 {
diff = params.MinimumDifficulty
}
periodCount := new(big.Int).Add(parentNumber, common.Big1)
periodCount.Div(periodCount, ExpDiffPeriod)
if periodCount.Cmp(common.Big1) > 0 {
// diff = diff + 2^(periodCount - 2)
expDiff := periodCount.Sub(periodCount, common.Big2)
expDiff.Exp(common.Big2, expDiff, nil)
diff.Add(diff, expDiff)
diff = common.BigMax(diff, params.MinimumDifficulty)
}
return diff
}
// jitCalculateGasAndSize 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 jitCalculateGasAndSize(env Environment, contract *Contract, instr instruction, statedb Database, mem *Memory, stack *stack) (*big.Int, *big.Int, error) {
var (
gas = new(big.Int)
newMemSize *big.Int = new(big.Int)
)
err := jitBaseCheck(instr, stack, gas)
if err != nil {
return nil, nil, err
}
// stack Check, memory resize & gas phase
switch op := instr.op; 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]
add := new(big.Int)
gas.Add(gas, params.LogGas)
gas.Add(gas, add.Mul(big.NewInt(int64(n)), params.LogTopicGas))
gas.Add(gas, add.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(contract.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)) {
g = params.SstoreSetGas
} else if !common.EmptyHash(val) && common.EmptyHash(common.BigToHash(y)) {
statedb.AddRefund(params.SstoreRefundGas)
g = params.SstoreClearGas
} else {
g = params.SstoreClearGas
}
gas.Set(g)
case SUICIDE:
if !statedb.IsDeleted(contract.Address()) {
statedb.AddRefund(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.Db().GetStateObject(common.BigToAddress(stack.data[stack.len()-2])) == nil {
if !env.Db().Exist(common.BigToAddress(stack.data[stack.len()-2])) {
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)
}
quadMemGas(mem, newMemSize, gas)
return newMemSize, gas, nil
}