// CalcGasLimit computes the gas limit of the next block after parent. It aims
// to keep the baseline gas close to the provided target, and increase it towards
// the target if the baseline gas is lower.
func CalcGasLimit(parentGasLimit, desiredLimit uint64) uint64 {
    delta := parentGasLimit/params.GasLimitBoundDivisor - 1
    limit := parentGasLimit
    if desiredLimit < params.MinGasLimit {
        desiredLimit = params.MinGasLimit
    }
    // If we're outside our allowed gas range, we try to hone towards them
    if limit < desiredLimit {
        limit = parentGasLimit + delta
        if limit > desiredLimit {
            limit = desiredLimit
        }
        return limit
    }
    if limit > desiredLimit {
        limit = parentGasLimit - delta
        if limit < desiredLimit {
            limit = desiredLimit
        }
    }
    return limit
}