int inc(int a) { int mask = ~a; /* Assuming a is 32-bit. If 64-bit, add 32-bit shift. */ mask |= mask << 1; mask |= mask << 2; mask |= mask

int inc(int a) { int mask = ~a; /* Assuming a is 32-bit. If 64-bit, add 32-bit shift. */ mask |= mask << 1; mask |= mask << 2; mask |= mask << 4; mask |= mask << 8; mask |= mask << 16; /* Take the longest run of 1s from the right of a. * mask has 0s there and 1s everywhere else. We want * to set the next bit to 1 and set the ones after * to 0. */ return (a | ~(mask << 1)) & mask; }