cache num active fps

proto/babylon/btcstaking/v1/incentive.proto

@@ -9,9 +9,13 @@ option go_package = "github.com/babylonlabs-io/babylon/x/btcstaking/types";
 // VotingPowerDistCache is the cache for voting power distribution of finality providers
 // and their BTC delegations at a height
 message VotingPowerDistCache {
+    option (gogoproto.goproto_getters) = false;
+    // total_voting_power is the total voting power of all the finality providers in the cache
     uint64 total_voting_power = 1;
     // finality_providers is a list of finality providers' voting power information
     repeated FinalityProviderDistInfo finality_providers = 2;
+    // num_active_fps is the number of finality providers that have positive voting power
+    uint32 num_active_fps = 3;
 }
 
 // FinalityProviderDistInfo is the reward distribution of a finality provider and its BTC delegations

x/btcstaking/keeper/power_dist_change.go

@@ -77,7 +77,6 @@ func (k Keeper) recordVotingPowerAndCache(ctx context.Context, dc *types.VotingP
 	for i := uint32(0); i < dc.GetNumActiveFPs(maxActiveFps); i++ {
 		fp := dc.FinalityProviders[i]
 		k.SetVotingPower(ctx, fp.BtcPk.MustMarshal(), babylonTipHeight, fp.TotalVotingPower)
-
 	}
 
 	// set the voting power distribution cache of the current height

x/btcstaking/keeper/voting_power_table_test.go

@@ -210,7 +210,7 @@ func FuzzVotingPowerTable_ActiveFinalityProviders(f *testing.F) {
 		maxActiveFpsParam := h.BTCStakingKeeper.GetParams(h.Ctx).MaxActiveFinalityProviders
 		// get a map of expected active finality providers
 		types.SortFinalityProviders(fpsWithMeta)
-		expectedActiveFps := fpsWithMeta[:min(uint32(len(fpsWithMeta)), maxActiveFpsParam)]
+		expectedActiveFps := fpsWithMeta[:min(uint32(len(fpsWithMeta)-len(noTimestampedFps)), maxActiveFpsParam)]
 		expectedActiveFpsMap := map[string]uint64{}
 		for _, fp := range expectedActiveFps {
 			expectedActiveFpsMap[fp.BtcPk.MarshalHex()] = fp.TotalVotingPower

x/btcstaking/types/incentive.go

@@ -40,17 +40,33 @@ func (dc *VotingPowerDistCache) FindNewActiveFinalityProviders(prevDc *VotingPow
 func (dc *VotingPowerDistCache) ApplyActiveFinalityProviders(maxActiveFPs uint32) {
 	// reset total voting power
 	dc.TotalVotingPower = 0
+
 	// sort finality providers
 	SortFinalityProviders(dc.FinalityProviders)
-	// calculate voting power of top N finality providers
-	numActiveFPs := dc.GetNumActiveFPs(maxActiveFPs)
-	for i := uint32(0); i < numActiveFPs; i++ {
+
+	// calculate voting power and get top N active finality providers
+	dc.calculateNumActiveFps()
+	for i := uint32(0); i < dc.GetNumActiveFPs(maxActiveFPs); i++ {
 		dc.TotalVotingPower += dc.FinalityProviders[i].TotalVotingPower
 	}
 }
 
 func (dc *VotingPowerDistCache) GetNumActiveFPs(maxActiveFPs uint32) uint32 {
-	return min(maxActiveFPs, uint32(len(dc.FinalityProviders)))
+	return min(maxActiveFPs, dc.NumActiveFps)
+}
+
+// calculateNumActiveFps iterates all the finality providers in the cache, calculates
+// the number of finality providers with positive voting power, and stores it in the
+// cache
+func (dc *VotingPowerDistCache) calculateNumActiveFps() {
+	activeCount := uint32(0)
+	for _, fp := range dc.FinalityProviders {
+		if fp.TotalVotingPower > 0 {
+			activeCount++
+		}
+	}
+
+	dc.NumActiveFps = activeCount
 }
 
 // GetActiveFinalityProviderSet returns a set of active finality providers

x/finality/README.md

@@ -271,8 +271,6 @@ Upon `MsgAddFinalitySig`, a Babylon node will execute as follows:
 
 1. Ensure the finality provider has been registered in Babylon and is not
    slashed.
-2. Ensure the epoch that the finality provider is registered has been finalized
-   by BTC timestamping.
 3. Ensure the finality provider has voting power at this height.
 4. Ensure the finality provider has not previously casted the same vote.
 5. Derive the EOTS public randomness using the committed EOTS master public