R4R: Decrease gas consumption by logarithm

app/v1/auth/ante.go

@@ -14,14 +14,13 @@ import (
 )
 
 const (
-	BlockStoreCostPerByte = 10
-	ed25519VerifyCost     = 59
-	secp256k1VerifyCost   = 100
-	maxMemoCharacters     = 100
-	// how much gas = 1 atom
-	gasPerUnitCost = 1000
-	// max total number of sigs per tx
-	txSigLimit = 7
+	ed25519VerifyCost   = 59
+	secp256k1VerifyCost = 100
+
+	// if gas > gasShift, gas = log(gas)/log(gasBase)
+	// else gasConsumed = gas
+	gasBase  = 1.02 // gas logarithm base
+	gasShift = 285  // gas logarithm shift
 )
 
 // NewAnteHandler returns an AnteHandler that checks
@@ -308,7 +307,7 @@ func setGasMeter(simulate bool, ctx sdk.Context, gasLimit uint64) sdk.Context {
 	if simulate || ctx.BlockHeight() == 0 {
 		return ctx.WithGasMeter(sdk.NewInfiniteGasMeter())
 	}
-	return ctx.WithGasMeter(sdk.NewGasMeter(gasLimit))
+	return ctx.WithGasMeter(sdk.NewGasMeterWithBase(gasLimit, gasBase, gasShift))
 }
 
 func getSignBytesList(chainID string, stdTx StdTx, stdSigs []StdSignature) (signatureBytesList [][]byte) {

types/gas.go

@@ -1,5 +1,9 @@
 package types
 
+import (
+	"math"
+)
+
 // Gas consumption descriptors.
 const (
 	GasIterNextCostFlatDesc = "IterNextFlat"
@@ -44,6 +48,8 @@ type GasMeter interface {
 type basicGasMeter struct {
 	limit    Gas
 	consumed Gas
+	base     float64
+	shift    uint64
 }
 
 // NewGasMeter returns a reference to a new basicGasMeter.
@@ -54,6 +60,15 @@ func NewGasMeter(limit Gas) GasMeter {
 	}
 }
 
+func NewGasMeterWithBase(limit Gas, base float64, shift uint64) GasMeter {
+	return &basicGasMeter{
+		limit:    limit,
+		consumed: 0,
+		base:     base,
+		shift:    shift,
+	}
+}
+
 func (g *basicGasMeter) GasConsumed() Gas {
 	return g.consumed
 }
@@ -70,6 +85,12 @@ func (g *basicGasMeter) GasConsumedToLimit() Gas {
 
 func (g *basicGasMeter) ConsumeGas(amount Gas, descriptor string) {
 	var overflow bool
+
+	// amount = log(gas)/log(gasBase)
+	if g.base > 1 && amount > g.shift && amount < math.MaxInt64 &&
+		(descriptor == GasWritePerByteDesc || descriptor == GasReadPerByteDesc) {
+		amount = uint64(math.Log(float64(int64(amount))) / math.Log(g.base))
+	}
 	// TODO: Should we set the consumed field after overflow checking?
 	g.consumed, overflow = AddUint64Overflow(g.consumed, amount)
 	if overflow {

types/gas_test.go

@@ -43,3 +43,34 @@ func TestGasMeter(t *testing.T) {
 
 	}
 }
+
+func TestGasMeterWithLog(t *testing.T) {
+	cases := []struct {
+		limit  Gas
+		usage  Gas
+		base   float64
+		shift  uint64
+		desc   string
+		expect Gas
+	}{
+		{1000, 100, 10, 0, GasWritePerByteDesc, 2},
+		{1000, 285, 1.02, 285, GasWritePerByteDesc, 285},
+		{1000, 286, 1.02, 285, GasWritePerByteDesc, 285},
+		{1000, 288, 1.02, 285, GasWritePerByteDesc, 285},
+		{1000, 289, 1.02, 285, GasWritePerByteDesc, 286},
+		{1000, 100, 10, 100, GasWritePerByteDesc, 100},
+		{1000, 100, 10, 0, GasReadPerByteDesc, 2},
+		{1000, 100, 10, 0, "", 100},
+		{1000, 100, 1, 0, GasWritePerByteDesc, 100},
+		{1000, 100, 0, 0, GasWritePerByteDesc, 100},
+		{1000, 100, 0.99, 0, GasWritePerByteDesc, 100},
+		{1000, 100, -0.1, 0, GasWritePerByteDesc, 100},
+	}
+
+	for tcnum, tc := range cases {
+		meter := NewGasMeterWithBase(tc.limit, tc.base, tc.shift)
+
+		meter.ConsumeGas(tc.usage, tc.desc)
+		require.Equal(t, tc.expect, meter.GasConsumed(), "Gas consumption not match. tc #%d", tcnum)
+	}
+}