// getData returns a slice from the data based on the start and size and pads
// up to size with zero's. This function is overflow safe.
func getData(data []byte, start, size *big.Int) []byte {
dlen := big.NewInt(int64(len(data)))
s := common.BigMin(start, dlen)
e := common.BigMin(new(big.Int).Add(s, size), dlen)
return common.RightPadBytes(data[s.Uint64():e.Uint64()], int(size.Uint64()))
}
// 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
}
func (self *StateTransition) refundGas() {
// Return eth for remaining gas to the sender account,
// exchanged at the original rate.
sender, _ := self.from() // err already checked
remaining := new(big.Int).Mul(self.gas, self.gasPrice)
sender.AddBalance(remaining)
// Apply refund counter, capped to half of the used gas.
uhalf := remaining.Div(self.gasUsed(), common.Big2)
refund := common.BigMin(uhalf, self.state.GetRefund())
self.gas.Add(self.gas, refund)
self.state.AddBalance(sender.Address(), refund.Mul(refund, self.gasPrice))
// Also return remaining gas to the block gas counter so it is
// available for the next transaction.
self.gp.AddGas(self.gas)
}