Question

How can I set, clear, and toggle a bit?

Answer 1

Setting a bit

Use the bitwise OR operator (|) to set nth bit of number to 1.

// Can be whatever unsigned integer type you want, but // it's important to use the same type everywhere to avoid // performance issues caused by mixing integer types. typedef unsigned long Uint;  // In C++, this can be template. // In C11, you can make it generic with _Generic, or with macros prior to C11. inline Uint bit_set(Uint number, Uint n) {     return number | ((Uint)1 << n); } 

Note that it’s undefined behavior to shift by more than the width of a Uint. The same applies to all remaining examples.

Clearing a bit

Use the bitwise AND operator (&) to set the nth bit of number to 0.

inline Uint bit_clear(Uint number, Uint n) {     return number & ~((Uint)1 << n); } 

You must invert the bit string with the bitwise NOT operator (~), then AND it.

Toggling a bit

Use the bitwise XOR operator (^) to toggle the nth bit of number.

inline Uint bit_toggle(Uint number, Uint n) {     return number ^ ((Uint)1 << n); } 

Checking a bit

You didn’t ask for this, but I might as well add it.

To check a bit, shift number n to the right, then bitwise AND it:

// bool requires #include <stdbool.h> prior to C23 inline bool bit_check(Uint number, Uint n) {     return (number >> n) & (Uint)1; } 

Changing the nth bit to x

There are alternatives with worse codegen, but the best way is to clear the bit like in bit_clear, then set the bit to value, similar to bit_set.

inline Uint bit_set_to(Uint number, Uint n, bool x) {     return (number & ~((Uint)1 << n)) | ((Uint)x << n); } 

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All solutions have been tested to provide optimal codegen with GCC and clang. See https://godbolt.org/z/Wfzh8xsjW.