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slot_epoch.go
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slot_epoch.go
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package helpers
import (
"fmt"
"time"
"github.com/pkg/errors"
stateTrie "github.com/prysmaticlabs/prysm/beacon-chain/state"
"github.com/prysmaticlabs/prysm/shared/mathutil"
"github.com/prysmaticlabs/prysm/shared/params"
"github.com/prysmaticlabs/prysm/shared/roughtime"
)
// MaxSlotBuffer specifies the max buffer given to slots from
// incoming objects. (24 mins with mainnet spec)
const MaxSlotBuffer = uint64(1 << 7)
// SlotToEpoch returns the epoch number of the input slot.
//
// Spec pseudocode definition:
// def compute_epoch_of_slot(slot: Slot) -> Epoch:
// """
// Return the epoch number of ``slot``.
// """
// return Epoch(slot // SLOTS_PER_EPOCH)
func SlotToEpoch(slot uint64) uint64 {
return slot / params.BeaconConfig().SlotsPerEpoch
}
// CurrentEpoch returns the current epoch number calculated from
// the slot number stored in beacon state.
//
// Spec pseudocode definition:
// def get_current_epoch(state: BeaconState) -> Epoch:
// """
// Return the current epoch.
// """
// return compute_epoch_of_slot(state.slot)
func CurrentEpoch(state *stateTrie.BeaconState) uint64 {
return SlotToEpoch(state.Slot())
}
// PrevEpoch returns the previous epoch number calculated from
// the slot number stored in beacon state. It also checks for
// underflow condition.
//
// Spec pseudocode definition:
// def get_previous_epoch(state: BeaconState) -> Epoch:
// """`
// Return the previous epoch (unless the current epoch is ``GENESIS_EPOCH``).
// """
// current_epoch = get_current_epoch(state)
// return GENESIS_EPOCH if current_epoch == GENESIS_EPOCH else Epoch(current_epoch - 1)
func PrevEpoch(state *stateTrie.BeaconState) uint64 {
currentEpoch := CurrentEpoch(state)
if currentEpoch == 0 {
return 0
}
return currentEpoch - 1
}
// NextEpoch returns the next epoch number calculated from
// the slot number stored in beacon state.
func NextEpoch(state *stateTrie.BeaconState) uint64 {
return SlotToEpoch(state.Slot()) + 1
}
// StartSlot returns the first slot number of the
// current epoch.
//
// Spec pseudocode definition:
// def compute_start_slot_at_epoch(epoch: Epoch) -> Slot:
// """
// Return the start slot of ``epoch``.
// """
// return Slot(epoch * SLOTS_PER_EPOCH)
func StartSlot(epoch uint64) (uint64, error) {
slot, err := mathutil.Mul64(epoch, params.BeaconConfig().SlotsPerEpoch)
if err != nil {
return slot, errors.Errorf("start slot calculation overflows: %v", err)
}
return slot, nil
}
// IsEpochStart returns true if the given slot number is an epoch starting slot
// number.
func IsEpochStart(slot uint64) bool {
return slot%params.BeaconConfig().SlotsPerEpoch == 0
}
// IsEpochEnd returns true if the given slot number is an epoch ending slot
// number.
func IsEpochEnd(slot uint64) bool {
return IsEpochStart(slot + 1)
}
// SlotsSinceEpochStarts returns number of slots since the start of the epoch.
func SlotsSinceEpochStarts(slot uint64) uint64 {
return slot % params.BeaconConfig().SlotsPerEpoch
}
// VerifySlotTime validates the input slot is not from the future.
func VerifySlotTime(genesisTime uint64, slot uint64, timeTolerance time.Duration) error {
slotTime, err := SlotToTime(genesisTime, slot)
if err != nil {
return err
}
// Defensive check to ensure unreasonable slots are rejected
// straight away.
if err := ValidateSlotClock(slot, genesisTime); err != nil {
return err
}
currentTime := roughtime.Now()
diff := slotTime.Sub(currentTime)
if diff > timeTolerance {
return fmt.Errorf("could not process slot from the future, slot time %s > current time %s", slotTime, currentTime)
}
return nil
}
// SlotToTime takes the given slot and genesis time to determine the start time of the slot.
func SlotToTime(genesisTimeSec uint64, slot uint64) (time.Time, error) {
timeSinceGenesis, err := mathutil.Mul64(slot, params.BeaconConfig().SecondsPerSlot)
if err != nil {
return time.Unix(0, 0), fmt.Errorf("slot (%d) is in the far distant future: %v", slot, err)
}
sTime, err := mathutil.Add64(genesisTimeSec, timeSinceGenesis)
if err != nil {
return time.Unix(0, 0), fmt.Errorf("slot (%d) is in the far distant future: %v", slot, err)
}
return time.Unix(int64(sTime), 0), nil
}
// SlotsSince computes the number of time slots that have occurred since the given timestamp.
func SlotsSince(time time.Time) uint64 {
return CurrentSlot(uint64(time.Unix()))
}
// CurrentSlot returns the current slot as determined by the local clock and
// provided genesis time.
func CurrentSlot(genesisTimeSec uint64) uint64 {
now := roughtime.Now().Unix()
genesis := int64(genesisTimeSec)
if now < genesis {
return 0
}
return uint64(now-genesis) / params.BeaconConfig().SecondsPerSlot
}
// ValidateSlotClock validates a provided slot against the local
// clock to ensure slots that are unreasonable are returned with
// an error.
func ValidateSlotClock(slot uint64, genesisTimeSec uint64) error {
maxPossibleSlot := CurrentSlot(genesisTimeSec) + MaxSlotBuffer
// Defensive check to ensure that we only process slots up to a hard limit
// from our local clock.
if slot > maxPossibleSlot {
return fmt.Errorf("slot %d > %d which exceeds max allowed value relative to the local clock", slot, maxPossibleSlot)
}
return nil
}
// RoundUpToNearestEpoch rounds up the provided slot value to the nearest epoch.
func RoundUpToNearestEpoch(slot uint64) uint64 {
if slot%params.BeaconConfig().SlotsPerEpoch != 0 {
slot -= slot % params.BeaconConfig().SlotsPerEpoch
slot += params.BeaconConfig().SlotsPerEpoch
}
return slot
}
// WeakSubjectivityCheckptEpoch returns the epoch of the latest weak subjectivity checkpoint for the active validator count and
// finalized epoch.
//
// Reference spec implementation:
// https://notes.ethereum.org/@adiasg/weak-subjectvity-eth2#Updating-Weak-Subjectivity-Checkpoint-States
func WeakSubjectivityCheckptEpoch(valCount uint64, fEpoch uint64) uint64 {
weakSubMod := params.BeaconConfig().MinValidatorWithdrawabilityDelay
m := params.BeaconConfig().MinPerEpochChurnLimit
q := params.BeaconConfig().ChurnLimitQuotient
d := params.BeaconConfig().SafetyDecay
churnMultiplier := m * q
if valCount >= churnMultiplier {
v := 256 * ((d * q / 2) / 256)
weakSubMod += v
} else {
v := 256 * ((d * valCount / (2 * m)) / 256)
weakSubMod += v
}
return fEpoch / weakSubMod
}