bitmask

Bitmask is a value, usually an unsigned integer, whose individual bits encode boolean flags. It is used to store and manipulate sets of options, permissions, or features in a compact form. Each bit position corresponds to a specific flag; a 1 indicates the flag is enabled, and a 0 indicates it is disabled.

Bitwise operations are used to manipulate masks. Setting bits typically uses OR, for example value |= mask. Clearing bits uses AND with the complement of the mask, as in value &= ~mask. Toggling bits uses XOR, value ^= mask. Checking bits uses AND, for instance (value & mask) != 0.

Creating masks begins with single-bit masks such as 1 << n, which yields a mask with only bit n set. Multi-bit masks can select groups of bits, such as a mask for the lowest four bits (0x0F) or a mask for specific positions defined by combining single-bit masks.

Common sizes include 8-, 16-, 32-, and 64-bit masks, typically stored in unsigned integers. In hexadecimal notation, masks are often written as 0x01, 0x02, 0x04, 0x08, and so on.

Examples illustrate usage. A file permission field might use bit 0 for read, bit 1 for write, and bit 2 for execute; a mask of 0x07 enables the first three permissions. To check if write permission is set, evaluate (perm & 0x02) != 0. Bitmasks are widely used in software for configuration flags, resource permissions, networking options, graphics, and embedded systems.