Gas multiplier getter (#492)

## Describe your changes and provide context
Allow multiplier to be read to make it easier to create new gas meters
with the same multiplier

## Testing performed to validate your change
unit tests

store/types/gas.go

@@ -51,6 +51,7 @@ type GasMeter interface {
 	IsPastLimit() bool
 	IsOutOfGas() bool
 	String() string
+	Multiplier() (numerator uint64, denominator uint64)
 }
 
 type basicGasMeter struct {
@@ -164,6 +165,10 @@ func (g *basicGasMeter) String() string {
 	return fmt.Sprintf("BasicGasMeter:\n  limit: %d\n  consumed: %d", g.limit, g.consumed)
 }
 
+func (g *basicGasMeter) Multiplier() (numerator uint64, denominator uint64) {
+	return 1, 1
+}
+
 type multiplierGasMeter struct {
 	basicGasMeter
 	multiplierNumerator   uint64
@@ -194,6 +199,10 @@ func (g *multiplierGasMeter) RefundGas(amount Gas, descriptor string) {
 	g.basicGasMeter.RefundGas(g.adjustGas(amount), descriptor)
 }
 
+func (g *multiplierGasMeter) Multiplier() (numerator uint64, denominator uint64) {
+	return g.multiplierNumerator, g.multiplierDenominator
+}
+
 type infiniteGasMeter struct {
 	consumed Gas
 	lock     *sync.Mutex
@@ -272,6 +281,10 @@ func (g *infiniteGasMeter) String() string {
 	return fmt.Sprintf("InfiniteGasMeter:\n  consumed: %d", g.consumed)
 }
 
+func (g *infiniteGasMeter) Multiplier() (numerator uint64, denominator uint64) {
+	return 1, 1
+}
+
 type infiniteMultiplierGasMeter struct {
 	infiniteGasMeter
 	multiplierNumerator   uint64
@@ -301,6 +314,10 @@ func (g *infiniteMultiplierGasMeter) RefundGas(amount Gas, descriptor string) {
 	g.infiniteGasMeter.RefundGas(g.adjustGas(amount), descriptor)
 }
 
+func (g *infiniteMultiplierGasMeter) Multiplier() (numerator uint64, denominator uint64) {
+	return g.multiplierNumerator, g.multiplierDenominator
+}
+
 type noConsumptionInfiniteGasMeter struct {
 	infiniteGasMeter
 }

store/types/gas_test.go

@@ -23,6 +23,9 @@ func TestInfiniteGasMeter(t *testing.T) {
 	meter.ConsumeGas(Gas(math.MaxUint64/2), "consume half max uint64")
 	require.Panics(t, func() { meter.ConsumeGas(Gas(math.MaxUint64/2)+2, "panic") })
 	require.Panics(t, func() { meter.RefundGas(meter.GasConsumed()+1, "refund greater than consumed") })
+	n, d := meter.Multiplier()
+	require.Equal(t, uint64(1), n)
+	require.Equal(t, uint64(1), d)
 }
 
 func TestGasMeter(t *testing.T) {
@@ -68,6 +71,9 @@ func TestGasMeter(t *testing.T) {
 		meter2 := NewGasMeter(math.MaxUint64)
 		meter2.ConsumeGas(Gas(math.MaxUint64/2), "consume half max uint64")
 		require.Panics(t, func() { meter2.ConsumeGas(Gas(math.MaxUint64/2)+2, "panic") })
+		n, d := meter.Multiplier()
+		require.Equal(t, uint64(1), n)
+		require.Equal(t, uint64(1), d)
 	}
 }
 
@@ -104,6 +110,10 @@ func TestMultiplierGasMeter(t *testing.T) {
 				require.True(t, meter.IsOutOfGas(), "At limit but got IsOutOfGas() false")
 			}
 		}
+
+		n, d := meter.Multiplier()
+		require.Equal(t, tc.multiplierNumerator, n)
+		require.Equal(t, tc.multiplierDenominator, d)
 	}
 }
 
@@ -135,6 +145,10 @@ func TestInfiniteMultiplierGasMeter(t *testing.T) {
 			require.False(t, meter.IsPastLimit(), "Not exceeded limit but got IsPastLimit() true")
 			require.False(t, meter.IsOutOfGas(), "Not yet at limit but got IsOutOfGas() true")
 		}
+
+		n, d := meter.Multiplier()
+		require.Equal(t, tc.multiplierNumerator, n)
+		require.Equal(t, tc.multiplierDenominator, d)
 	}
 }