// targetAdjustmentBase returns the magnitude that the target should be
// adjusted by before a clamp is applied.
func (cs *ConsensusSet) targetAdjustmentBase(blockMap *bolt.Bucket, pb *processedBlock) *big.Rat {
// Grab the block that was generated 'TargetWindow' blocks prior to the
// parent. If there are not 'TargetWindow' blocks yet, stop at the genesis
// block.
var windowSize types.BlockHeight
parent := pb.Block.ParentID
current := pb.Block.ID()
for windowSize = 0; windowSize < types.TargetWindow && parent != (types.BlockID{}); windowSize++ {
current = parent
copy(parent[:], blockMap.Get(parent[:])[:32])
}
timestamp := types.Timestamp(encoding.DecUint64(blockMap.Get(current[:])[40:48]))
// The target of a child is determined by the amount of time that has
// passed between the generation of its immediate parent and its
// TargetWindow'th parent. The expected amount of seconds to have passed is
// TargetWindow*BlockFrequency. The target is adjusted in proportion to how
// time has passed vs. the expected amount of time to have passed.
//
// The target is converted to a big.Rat to provide infinite precision
// during the calculation. The big.Rat is just the int representation of a
// target.
timePassed := pb.Block.Timestamp - timestamp
expectedTimePassed := types.BlockFrequency * windowSize
return big.NewRat(int64(timePassed), int64(expectedTimePassed))
}
// setChildTarget computes the target of a blockNode's child. All children of a node
// have the same target.
func (cs *ConsensusSet) setChildTarget(blockMap *bolt.Bucket, pb *processedBlock) {
// Fetch the parent block.
var parent processedBlock
parentBytes := blockMap.Get(pb.Block.ParentID[:])
err := encoding.Unmarshal(parentBytes, &parent)
if build.DEBUG && err != nil {
panic(err)
}
if pb.Height%(types.TargetWindow/2) != 0 {
pb.ChildTarget = parent.ChildTarget
return
}
adjustment := clampTargetAdjustment(cs.targetAdjustmentBase(blockMap, pb))
adjustedRatTarget := new(big.Rat).Mul(parent.ChildTarget.Rat(), adjustment)
pb.ChildTarget = types.RatToTarget(adjustedRatTarget)
}