22711100011
AND 2(Bitmask)00000010
Result00000010
Bit 2 of the mask, matches bit 2 of the number and it is **1** therefore **10** is returned (binary equivalent of decimal **2**) Bitwise OR (**|**) will return **1** in any position if at least one bit of the two numbers is the same position is **1** and **0** if both are set to **0**. For example: ``` PRINT %@10101010 | @01101011 ``` will return **235** as only bits in positions 3 and 5 in both numbers are set to **0** making the resulting number **11101011** in binary form (or **235** in decimal). To better illustrate:
17010101010
OR 107(Bitmask)01101011
Result11101011
Finally, bitwise XOR (↑|) will only return **1** in any position if either bit is set to **1** but *not both*. So two 0s *and* two 1s, both return **0** in a position. Using the same numbers as in the previous example: ``` PRINT %@10101010 ↑| @01101011 ``` will return **193** or binary **1100001** since:
17010101010
XOR 107(Bitmask)01101011
Result11000001
Bitwise expressions are uniquely helpful in determining the condition of flags in several of the ZX Spectrum Next ports (as we will see in *Chapter 22*), since these take the form of individual bits in a binary number and testing those with regular arithmetic can be cumbersome and slow. ### Signed vs Unsigned Integer Expressions As you saw in *Chapter 1* and in the introduction to this chapter, integer variables in *NextBASIC* are fixed to 16-bits wide *unsigned*, which means that they can display *only positive* integers from **0** to **65535**. To illustrate approximately what that means, try the following: ``` PRINT %-64448 ``` The computer will respond with: **1088**. Keep this result in mind for a moment and then try: ``` PRINT %-32448 ``` This time the computer will display the number **33088** on screen. Are you confused yet? Maybe seeing the numbers in binary will help. Let's start with the first response of **1088** and we'll work backwards. | Decimal | Binary | | |---|---|---| | **1088** | **0000 0100 0100 0000** | | | **-64448** | **1 0000 0100 0100 0000** | | | **64447** | **1111 1011 1011 1111** | Don't mind this for now! | Aha! Let's now see the second response: