Is it possible to have a 64bit Integer addition in C?

"i hope you can show me a little example"

struct U64 {
    unsigned long msl;
    unsigned long lsl;
};

struct U64 U64_sum(struct U64 augend, struct U64 addend)
{
    struct U64 sum;

    sum.msl = augend.msl + addend.msl;
    sum.lsl = augend.lsl + addend.lsl;

    if (sum.lsl < augend.lsl)   /* Carry? */
        ++sum.msl;

    return sum;
}

"i hope you can show me a little example"

struct U64 {
    unsigned long msl;
    unsigned long lsl;
};

struct U64 U64_sum(struct U64 augend, struct U64 addend)
{
    struct U64 sum;

    sum.msl = augend.msl + addend.msl;
    sum.lsl = augend.lsl + addend.lsl;

    if (sum.lsl < augend.lsl)   /* Carry? */
        ++sum.msl;

    return sum;
}