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calculate.go
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calculate.go
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package effective
import (
"bytes"
"encoding/json"
"math/big"
"sort"
"github.com/PositionExchange/posichain/crypto/bls"
"github.com/PositionExchange/posichain/numeric"
"github.com/ethereum/go-ethereum/common"
)
// medium.com/harmony-one/introducing-harmonys-effective-proof-of-stake-epos-2d39b4b8d58
var (
two = numeric.NewDecFromBigInt(big.NewInt(2))
c, _ = numeric.NewDecFromStr("0.15")
cV2, _ = numeric.NewDecFromStr("0.35")
onePlusC = numeric.OneDec().Add(c)
oneMinusC = numeric.OneDec().Sub(c)
onePlusCV2 = numeric.OneDec().Add(cV2)
oneMinusCV2 = numeric.OneDec().Sub(cV2)
)
// SlotPurchase ..
type SlotPurchase struct {
Addr common.Address
Key bls.SerializedPublicKey
RawStake numeric.Dec
EPoSStake numeric.Dec
}
// MarshalJSON ..
func (p SlotPurchase) MarshalJSON() ([]byte, error) {
return json.Marshal(struct {
Addr string `json:"slot-owner"`
Key string `json:"bls-public-key"`
RawStake numeric.Dec `json:"raw-stake"`
EPoSStake numeric.Dec `json:"eposed-stake"`
}{
p.Addr.Hex(),
p.Key.Hex(),
p.RawStake,
p.EPoSStake,
})
}
// SlotOrder ..
type SlotOrder struct {
Stake *big.Int `json:"stake"`
SpreadAmong []bls.SerializedPublicKey `json:"keys-at-auction"`
Percentage numeric.Dec `json:"percentage-of-total-auction-stake"`
}
// Median ..
func Median(stakes []SlotPurchase) numeric.Dec {
if len(stakes) == 0 {
return numeric.ZeroDec()
}
sort.SliceStable(
stakes,
func(i, j int) bool {
return stakes[i].RawStake.GT(stakes[j].RawStake)
},
)
const isEven = 0
switch l := len(stakes); l % 2 {
case isEven:
left := (l / 2) - 1
right := l / 2
return stakes[left].RawStake.Add(stakes[right].RawStake).Quo(two)
default:
return stakes[l/2].RawStake
}
}
// Compute ..
func Compute(
shortHand map[common.Address]*SlotOrder, pull int,
) (numeric.Dec, []SlotPurchase) {
eposedSlots := []SlotPurchase{}
if len(shortHand) == 0 {
return numeric.ZeroDec(), eposedSlots
}
type t struct {
addr common.Address
slot *SlotOrder
}
shorter := []t{}
for key, value := range shortHand {
shorter = append(shorter, t{key, value})
}
sort.SliceStable(
shorter,
func(i, j int) bool {
return bytes.Compare(
shorter[i].addr.Bytes(), shorter[j].addr.Bytes(),
) == -1
},
)
// Expand
for _, staker := range shorter {
slotsCount := len(staker.slot.SpreadAmong)
if slotsCount == 0 {
continue
}
spread := numeric.NewDecFromBigInt(staker.slot.Stake).
QuoInt64(int64(slotsCount))
for i := 0; i < slotsCount; i++ {
eposedSlots = append(eposedSlots, SlotPurchase{
Addr: staker.addr,
Key: staker.slot.SpreadAmong[i],
// NOTE these are same because later the .EPoSStake mutated
RawStake: spread,
EPoSStake: spread,
})
}
}
sort.SliceStable(
eposedSlots,
func(i, j int) bool {
return eposedSlots[i].RawStake.GT(eposedSlots[j].RawStake)
},
)
if l := len(eposedSlots); l < pull {
pull = l
}
picks := eposedSlots[:pull]
if len(picks) == 0 {
return numeric.ZeroDec(), []SlotPurchase{}
}
return Median(picks), picks
}
// Apply ..
func Apply(shortHand map[common.Address]*SlotOrder, pull int, isExtendedBound bool) (
numeric.Dec, []SlotPurchase,
) {
median, picks := Compute(shortHand, pull)
max := onePlusC.Mul(median)
min := oneMinusC.Mul(median)
if isExtendedBound {
max = onePlusCV2.Mul(median)
min = oneMinusCV2.Mul(median)
}
for i := range picks {
picks[i].EPoSStake = effectiveStake(min, max, picks[i].RawStake)
}
return median, picks
}
func effectiveStake(min, max, actual numeric.Dec) numeric.Dec {
newMax := numeric.MinDec(max, actual)
return numeric.MaxDec(newMax, min)
}