What are the common bit mask patterns and how do you create them?

Build masks with shifts: 1 << n sets a single bit at position n, and (1 << n) - 1 makes the low n bits all 1s.

Common mask patterns:

Why (1 << n) - 1 gives n ones:

1 << 4     = 00010000  (16)
(1 << 4)-1 = 00001111  (15, four 1s!)

Practical examples:

// Get lower 4 bits (nibble)
low_nibble = value & 0x0F;           // & 00001111

// Get upper 4 bits of a byte
high_nibble = (value >> 4) & 0x0F;

// Check if bit 7 is set
if (value & (1 << 7)) { ... }

// Clear bits 4-6
value &= ~(0x70);                    // & 10001111

// Set bits 0-3 to a value (0-15)
result = (original & ~0x0F) | new_value;

Tip: Drawing out the binary pattern helps when designing masks. 4 bits = 1 hex digit.

Go deeper:

• Mask (computing) (Wikipedia) — using bitmasks to set, clear, toggle, and extract bits.