RtlLargeIntegerSubtract

LARGE_INTEGER
    RtlLargeIntegerSubtract(

        IN LARGE_INTEGER  Minuend,
        IN LARGE_INTEGER  Subtrahend
        );

RtlLargeIntegerSubtract is exported to support existing driver binaries and is obsolete.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