integral promotion

bitshift.cpp

#include <iostream>

union TileId_t
{
    uint64_t packed;

    struct {
        uint64_t  y : 28;
        uint64_t  x : 28;
        uint8_t   z :  8;
    };
};

int main() {
    TileId_t tid;
    tid.x = 133021696;
    tid.y = 135888896;
    tid.z = 15;
    std::cout << tid.packed << std::endl;

    uint64_t sx = static_cast<uint64_t>(tid.x) >> 8;
    uint64_t sy = static_cast<uint64_t>(tid.y) >> 8;
    uint64_t pid1 = (sx << 20) + sy;
    std::cout << "Variant 1 " << pid1 << std::endl;

    uint64_t pid2 = ((static_cast<uint64_t>(tid.x) >> 8) << 20) + (static_cast<uint64_t>(tid.y) >> 8);
    std::cout << "Variant 2 " << pid2 << std::endl;
}