common: adding Address.Equals

It's a common use-case to compare addresses.
Here we add the Equals method to the address type.
It uses for loop instead of bytes.Equals to avoid extra memory allocation.

common/types.go

@@ -165,6 +165,16 @@ func (a Address) Bytes() []byte { return a[:] }
 func (a Address) Big() *big.Int { return new(big.Int).SetBytes(a[:]) }
 func (a Address) Hash() Hash    { return BytesToHash(a[:]) }
 
+// Equals returns a boolean reporting whether a and b are the same addresses
+func (a Address) Equals(b Address) bool {
+	for i := 0; i < AddressLength; i++ {
+		if a[i] != b[i] {
+			return false
+		}
+	}
+	return true
+}
+
 // Hex returns an EIP55-compliant hex string representation of the address.
 func (a Address) Hex() string {
 	unchecksummed := hex.EncodeToString(a[:])

common/types_test.go

@@ -125,3 +125,24 @@ func BenchmarkAddressHex(b *testing.B) {
 		testAddr.Hex()
 	}
 }
+
+func TestAddressEquals(t *testing.T) {
+	var tests = []struct {
+		a1, a2 string
+		result bool
+	}{
+		{"0x5aaeb6053f3e94c9b9a09f33669435e7ef1beaed", "0x5aaeb6053f3e94c9b9a09f33669435e7ef1beaed", true},
+		{"0x5aaeb6053f3e94c9b9a09f33669435e7ef1beaed", "0x5AAEB6053f3e94c9b9a09f33669435e7ef1beaed", true},
+		{"0x0", "0x0000000000000000000000000000000000000000", true},
+		{"0x1aaeb6053f3e94c9b9a09f33669435e7ef1beaed", "0x5aaeb6053f3e94c9b9a09f33669435e7ef1beaed", false},
+		{"0x0", "0x5aaeb6053f3e94c9b9a09f33669435e7ef1beaed", false},
+	}
+	for i, test := range tests {
+		a1 := HexToAddress(test.a1)
+		a2 := HexToAddress(test.a2)
+		if a1.Equals(a2) != test.result {
+			t.Errorf("test #%d: failed. Should (%s == %s) be %v",
+				i, test.a1, test.a2, test.result)
+		}
+	}
+}