Bit Operations

Code

#include <stdio.h>
#include <stdint.h>

int main(void) {
    uint32_t flags = 0;

    #define FLAG_READ   (1u << 0)
    #define FLAG_WRITE  (1u << 1)
    #define FLAG_EXEC   (1u << 2)

    flags |= FLAG_READ | FLAG_WRITE;   // set
    printf("flags = 0x%x\n", flags);

    flags &= ~FLAG_WRITE;              // clear
    printf("flags = 0x%x\n", flags);

    int can_read = (flags & FLAG_READ) != 0;
    printf("can_read = %d\n", can_read);

    // Toggle
    flags ^= FLAG_EXEC;
    printf("flags = 0x%x\n", flags);

    // Shift and mask nibbles
    uint32_t v = 0xDEADBEEF;
    printf("nibble = 0x%x\n", (v >> 8) & 0xF);

    // Population count of a byte
    uint8_t b = 0b10110101;
    int count = __builtin_popcount(b);
    printf("popcount = %d\n", count);
    return 0;
}

Explanation

Bitwise operators set, clear, toggle, and test individual bits within an integer, which is how flags and hardware registers are packed. The pattern flags & ~MASK clears bits while flags | MASK sets them. Shifting right then masking extracts a field of width n at any offset.

More C Snippets