Bitwise operations tend to be confusing because it uses some of the more cryptic symbols on the keyboard and what they do is less clear.
Code:
& - AND
| - inclusive OR (This is a pipe, SHIFT-\)
^ - exclusive OR (XOR)
<< - left shift
>> - right shift
~ - one's complement
AND:
| Input 1 |
Input 2 |
Output |
| 0 |
0 |
0 |
| 0 |
1 |
0 |
| 1 |
0 |
0 |
| 1 |
1 |
1 |
Usage:
x = x & 0177;
This will set every bit above the bottom 7 to 0, then save the lower 7 to their original state.
INCLUSIVE OR:
| Input 1 |
Input 2 |
Output |
| 0 |
0 |
0 |
| 0 |
1 |
1 |
| 1 |
0 |
1 |
| 1 |
1 |
1 |
Usage:
x = x | 0177;
This will set the bottom 7 bits to 1, and retain the rest from x.
EXCLUSIVE OR (XOR):
| Input 1 |
Input 2 |
Output |
| 0 |
0 |
0 |
| 0 |
1 |
1 |
| 1 |
0 |
1 |
| 1 |
1 |
0 |
Note the difference from inclusive OR by its behavior with two 1 inputs.
Usage:
x = x ^ 0177;
This will reverse the bottom 7 bits of x.
The advantage of ^ versus | is that you can get the original input again by XORing with the same number.
x == ( (x ^ 0177) ^ 0177)
This property means that XOR is used extensively in encryption applications.
Sources:
The C Programming Language 2nd Ed., Kernighan & Ritchie, pg. 48-49.
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