avoid floating point math

chain/actors/actor_miner.go

@@ -3,7 +3,6 @@ package actors
 import (
 	"context"
 	"fmt"
-	"math"
 
 	"github.com/filecoin-project/go-lotus/build"
 	"github.com/filecoin-project/go-lotus/chain/actors/aerrors"
@@ -727,17 +726,9 @@ func (sma StorageMinerActor) SlashConsensusFault(act *types.Actor, vmctx types.V
 	// current GROWTH_RATE results in SLASHER_SHARE reaches 1 after 30 blocks
 	// TODO: define arithmetic precision and rounding for this operation
 	blockElapsed := vmctx.BlockHeight() - params.AtHeight
-	growthRate := 1.26
-	initialShare := 0.001
 
-	// REVIEW: floating point precision loss anyone?
+	slasherShare := slasherShare(params.SlashedCollateral, blockElapsed)
-	slasherPortion := initialShare * math.Pow(growthRate, float64(blockElapsed))
-	if slasherPortion > 1 {
-		slasherPortion = 1
-	}
 
-	const precision = 1000000
-	slasherShare := types.BigDiv(types.BigMul(types.NewInt(uint64(precision*slasherPortion)), slashedCollateral), types.NewInt(precision))
 	burnPortion := types.BigSub(slashedCollateral, slasherShare)
 
 	_, err := vmctx.Send(vmctx.Message().From, 0, slasherShare, nil)
@@ -759,3 +750,24 @@ func (sma StorageMinerActor) SlashConsensusFault(act *types.Actor, vmctx types.V
 
 	return nil, nil
 }
+
+func slasherShare(total types.BigInt, elapsed uint64) types.BigInt {
+	// [int(pow(1.26, n) * 10) for n in range(30)]
+	fracs := []uint64{10, 12, 15, 20, 25, 31, 40, 50, 63, 80, 100, 127, 160, 201, 254, 320, 403, 508, 640, 807, 1017, 1281, 1614, 2034, 2563, 3230, 4070, 5128, 6462, 8142}
+	const precision = 10000
+
+	var frac uint64
+	if elapsed >= uint64(len(fracs)) {
+		frac = precision
+	} else {
+		frac = fracs[elapsed]
+	}
+
+	return types.BigDiv(
+		types.BigMul(
+			types.NewInt(frac),
+			total,
+		),
+		types.NewInt(precision),
+	)
+}

gen/main.go

@@ -5,6 +5,7 @@ import (
 	"os"
 
 	"github.com/filecoin-project/go-lotus/chain/actors"
+	"github.com/filecoin-project/go-lotus/chain/types"
 	gen "github.com/whyrusleeping/cbor-gen"
 )