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:

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:

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.

Aha! Let's now see the second response: