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Miloslav Ciz 2023-01-15 15:55:54 +01:00
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@ -10,7 +10,7 @@ Basic bit manipulation techniques are common and part of general knowledge so th
- `&` (bitwise [AND](and.md)): Performs the logical AND on all corresponding bits of two operands, e.g. `0b0110 & 0b1100` gives 0100 (4 in decimal). This may be used to mask out specific bits, to check if specific bits are set (useful to check the set flags as mentioned above) or to clear (set to zero) specific bits. Consider the flag example from above, if we want to check if value *x* has e.g. the option B set, we simply do `x & OPTION_B` which results in non-zero value if the option is set. Another example may be `myNumber & 0b00001111` (in practice you'll see hexadecimal values, i.e. `myNumber & 0x0F`) which masks out the lowest 4 bits of *myNumber* (which is equivalent to the operation [modulo](mod.md) 16).
- `~` (bitwise [NOT](not.md)): Flips every bit of the number -- pretty straightforward. This is used e.g. for clearing bits as `x & ~(1 << 3)` (clear 3rd bit of *x*).
- `^` (bitwise [XOR](xor.md)): Performs the logical XOR on all corresponding bits of two operands, e.g. `0b0110 ^ 0b1100` gives 1010 (10 in decimal). This is used to e.g. flip specific bits.
- `<<` and `>>` (bitwise shift left/right): Performs bitwise shift left or right (WATCH OUT: shifting by data type width or more is undefined behavior in C). This is typically used to perform fast multiplication (left) and division (right) by powers of two (2, 4, 8, 16, ...), just as we can quickly multiply/divide by 10 in decimal by shifting the decimal point. E.g. `5 << 3` is the same as 5 * 2^3 = 5 * 8 = 40.
- `<<` and `>>` (binary shift left/right): Performs bitwise shift left or right (WATCH OUT: shifting by data type width or more is undefined behavior in C). This is typically used to perform fast multiplication (left) and division (right) by powers of two (2, 4, 8, 16, ...), just as we can quickly multiply/divide by 10 in decimal by shifting the decimal point. E.g. `5 << 3` is the same as 5 * 2^3 = 5 * 8 = 40.
## Specific Bit Hacks