Further simplify bitmasking lol

cerberus.go

@@ -43,7 +43,7 @@ func checkZeros(diff uint32, hash []byte) bool {
 		rem    = diff % 8         // Remainder after dividing diff (given in bits) to bytes.
 		nbytes = (diff - rem) / 8 // Amount of 0x0 bytes we can divide difficulty bits into.
 
-		// Bitmask by setting a 1 bit (on LHS) for each remaining bit to check.
+		// Create bitmask by setting a 1 bit (on LHS) for each remaining bit to check.
 		mask uint8 = ^((1 << (8 - rem)) - 1)
 		// Example (rem = 3): mask = ^((1 << (8 - 3)) - 1)
 		//                         = ^(00100000 - 1)
@@ -62,11 +62,12 @@ func checkZeros(diff uint32, hash []byte) bool {
 			return false
 		}
 	}
-	// If we don't have any more bits to check, return.
-	if rem == 0 {
-		return true
-	}
 
+	// For rem = 0: mask = ^((1 << 8) - 1)
+	//                   = ^(00000000 - 1) [note the uint8 wraparound]
+	//                   = ^(11111111) [note the uint8 wraparound again]
+	//                   = 00000000
+	// Cool, right?
 	return hash[nbytes]&mask == 0x0
 }
 

cerberus_test.go

@@ -118,6 +118,11 @@ func TestCheckZeros(t *testing.T) {
 		t.Error(errBadZeroCheck{d, h})
 	}
 
+	d, h = uint32(16), []byte{0, 0, 255, 128, 42}
+	if !checkZeros(d, h) {
+		t.Error(errBadZeroCheck{d, h})
+	}
+
 	// This should fail (i.e. be false).
 	d, h = uint32(3), []byte{33, 130, 222, 88}
 	if checkZeros(d, h) {