Question

I would like to avoid the if statement below. Can I somehow copy the set bits from the old bit array to the new one using only bitwise operators?

#define BYTE_POS(pos) (pos / CHAR_BIT)
#define BIT_POS(pos) (1 << (CHAR_BIT - 1 - (pos % CHAR_BIT)))

if ((old_array[BYTE_POS(old_pos)] & BIT_POS(old_pos)) != 0) {
    new_array[BYTE_POS(new_pos)] |= BIT_POS(new_pos);
}

Answer 1

Change BIT_POS to this:

#define BIT_POS(pos, state) (state << (CHAR_BIT - 1 - (pos % CHAR_BIT)))

then change the code to:

bool state = (old_array[BYTE_POS(old_pos)] & BIT_POS(old_pos, 1)) != 0);

new_array[BYTE_POS(new_pos)] |= BIT_POS(new_pos, state);