Bitmask

Bitmask

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Prerequisites

- Bit

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1. What is Bitmask?

Bitmasking is a technique that uses bits of an integer to represent multiple states. You can manage multiple boolean values using a single integer.

Example:

int i32Mask = 0;

Each bit represents a state:

bit:   3 2 1 0
       ↓ ↓ ↓ ↓
value: 1 0 1 1

2. Why use Bitmask?

✔ Memory efficient
✔ Very fast operations (bitwise)
✔ Great for representing combinations of states

👉 Common use cases:

• Subsets
• Visited checks (DFS/BFS)
• DP with state compression

3. How to use Bitmask

3-1. ON/OFF

✔ Turn ON a bit

mask |= (1 << i);

✔ Turn OFF a bit

mask &= ~(1 << i);

✔ Toggle a bit

mask ^= (1 << i);

✔ Check a bit

if (mask & (1 << i)) 
{
    // i-th bit is ON
}

✔ Reset all bits

mask = 0;

3-2. Management Enum

enum EStatus
{
    EStatus_None = 0x00,
    EStatus_Left = 0x01,    // 0b00001
    EStatus_Top = 0x02,     // 0b00010
    EStatus_Right = 0x04,   // 0b00100
    EStatus_Bottom = 0x08   // 0b01000
    EStatus_LT = EStatus_Left | EStatus_Top,    // 0b00011
    EStatus_LR = EStatus_Left | EStatus_Right,  // 0b00101
    EStatus_LB = EStatus_Left | EStatus_Bottom, // 0b01001
    ....
}