lowest_bits_set.cpp

lowest_bits_set.cpp

#include <bitset>
#include <cassert>
#include <iostream>

using MaskType = uint64_t;

static int LowestBitSet(const MaskType v)
{
    return __builtin_ffsl(v);
}

static MaskType RemoveLowestSetBit(MaskType v)
{
    assert(v != 0);
    return v & (v - 1);
}

static void PrintBits(const MaskType v)
{
    using namespace std;
    MaskType c = v;  // cursor

    cout << "decimal=" << v
         << " binary=" << bitset<sizeof(MaskType) * 8>(v)
         << " items=[ ";

    while (c != 0) {
        int i = LowestBitSet(c);
        cout << i << " ";
        c = RemoveLowestSetBit(c);
    }
    cout << "]" << endl;
}

int main()
{
    PrintBits(3);  // 011 = 1 and 2
    PrintBits(5);  // 101 = 1 and 3
    PrintBits(6);  // 110 = 2 and 3
    PrintBits(7);  // 111 = 1, 2, 3
}