RtlEnlargedUnsignedMultiply

LARGE_INTEGER
    RtlEnlargedUnsignedMultiply(

        IN ULONG  Multiplicand,
        IN ULONG  Multiplier
        );

RtlEnlargedUnsignedMultiply is exported to support existing driver binaries and is obsolete. For better performance, use the compiler support for 64-bit integer operations.