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Diffstat (limited to '03-04.md')
| -rw-r--r-- | 03-04.md | 91 |
1 files changed, 90 insertions, 1 deletions
@@ -168,5 +168,94 @@ int n; // n is 0000 0000 0000 1101 n << 1 //now n is 0000 0000 0001 1010 n << 4 //now n is 0000 0000 1101 0000 n >> 3 //now n is 0000 0000 0000 0001 -n << 4 //now n is 0000 0000 1101 0000 ``` + +- Compound assignment operators `<<=` and `>>=` + - cause the value resulting from the shift to be stored in the variable supplied as the left operand + +### Bitwise AND, XOR, and OR + +- The bitwise operators `&` (and), `^` (xor), and `|` (or) + - Take two operands that are viewed as strings of bits + - The operator determines each bit of the result by considering corresponding bits of each operand + - For each bit: + - `r = n & m` -> 1 when both n and m are 1 + - `r = n | m` -> 1 when n and/or m is 1 + - `r = n ^ m` -> 1 when n and m do not match + +- Example: + +``` +n = 0000 0000 0000 1101 +m = 0000 0000 0011 1100 +m & n = 0000 0000 0000 1100 + +n = 0000 0000 0000 1101 +m = 0000 0000 0011 1100 +m | n = 0000 0000 0011 1101 + +n = 0000 0000 0000 1101 +m = 0000 0000 0011 1100 +m ^ n = 0000 0000 0011 0001 +``` + +- Compound assignment operators `&=`, `|=`, `^=` + - cause the resulting value to be stored in the variable supplied as the left operand + +--- + +- Notes on shifting + - `<<` by 1 is the same as multiplying by 2 + - `>>` by 1 is the same as dividing by 2 +- Notes on `~` and `!` + - `~` and `!` are different operators + - `~` is a bitwise operator + - each bit is reversed + - `!` is a logical complement or negation + - `!nonzero` -> false (zero) + - `!zero` -> true (one) + +- Notes on AND + - `x & 0` is always 0 + - `x & 1` is always x +- Notes on OR + - `x | 1` is always 1 + - `x | 0` is always x + +- Masks -- Used to change specific bits in an integer + - To set specific bits + - Use OR with a mask in which only the bits to be set have 1: + +``` +short c = 0000 0101 +short mask = 0000 0010 +c | mask = 0000 0111 +``` + +- To zero specific bits + - Use AND with a mask in which only the bits to be zeroed have 0 + +``` +short c = 0000 0101 +short mask = 1111 1110 +c & mask = 0000 0100 +``` + +- To verify specific bit + - Use AND with a mask in which only the bit to be verified is 1 + - Result == 0 implied that bit == 0 + - Result != 0 implies that bit == 1 + +``` +short c = 0000 0101 +short mask = 0000 0100 +c & mask = 0000 0100 //not zero ==> bit is not zero +``` + +- Notes on XOR + - x ^ 0 is always x + - x ^ 1 is always ~x + - x ^ x is always 0 + - x ^ ~x is always 1 + - x ^ y == z, then + - x == z ^ y and y == z ^ x |