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c++bit-manipulationbit

Return bit positions without loops

Is there any way of finding bit positions without using loops (for/while) in C++, using std::bitset? Suppose we have a binary number 11001 and we'd like to find all 0s positions. Any sort of prebuilt, time-space efficient functions?

Solution

  • without using loops

    we have a binary number 11001 and we'd like to find all 0s positions

    Unroll the loop yourself.

    void check(unsigned pos, unsigned number, std::vector<unsigned>& out) {
    if (!(number & (1u << pos))) out.push_back(pos);
}
std::vector<unsigned> positions_of_0s(unsigned number) {
    std::vector<unsigned> ret;
    check(0, number, ret);
    check(1, number, ret);
    check(2, number, ret);
    check(3, number, ret);
    check(4, number, ret);
    return ret;
}