RtlConvertUlongToLuid - NtDoc

Native API online documentation, based on the System Informer (formerly Process Hacker) phnt headers 
#ifndef _NTRTL_H

FORCEINLINE
LUID
NTAPI_INLINE
RtlConvertUlongToLuid(
    _In_ ULONG Ulong
    )
{
    LUID tempLuid;

    tempLuid.LowPart = Ulong;
    tempLuid.HighPart = 0;

    return tempLuid;
}

#endif

View code on GitHub

This function is documented in Windows Driver Kit.

Edit description on GitHub