Why is this an issue?
Certain bitwise operations are not needed and should not be performed because their results are predictable.
Specifically, using And -1 with any value always results in the original value.
That is because the binary representation of -1 on a numeric data type
supporting negative numbers, such as Integer or Long, is based on two’s complement and made of all 1s: &B111…111.
Performing And between a value and &B111…111 means applying the And operator to each bit of the value
and the bit 1, resulting in a value equal to the provided one, bit by bit.
anyValue And -1 ' Noncompliant
anyValue ' Compliant
Similarly, anyValue Or 0 always results in anyValue, because the binary representation of 0 is always
&B000…000 and the Or operator returns its first input when the second is 0.
anyValue Or 0 ' Noncompliant
anyValue ' Compliant
The same applies to anyValue Xor 0: the Xor operator returns 1 when its two input bits are different
(1 and 0 or 0 and 1) and returns 0 when its two input bits are the same (both
0 or both 1). When Xor is applied with 0, the result would be 1 if the other input is
1, because the two input bits are different, and 0 if the other input bit is 0, because the two input are the
same. That results in returning anyValue.
anyValue Xor 0 ' Noncompliant
anyValue ' Compliant
Resources
Documentation
- Bitwise operations (C# reference)
- And Operator (Visual Basic)
- Or Operator (Visual Basic)
- Xor Operator (Visual Basic)
- Integral numeric types (C# reference)
- Numeric Data Types (Visual Basic)
- Two’s complement