Importing Kernel-Mode Safe Integer Functions
The kernel-mode safe integer functions are available as inline code that is contained in ntintsafe.h or in a library that you link your code to. This header file is available in the Windows Driver Kit (WDK).
It is important to note that you must use arithmetic operations on unsigned values. To use a signed value, you must use a conversion function to first convert the signed value to an unsigned value safely before using the arithmetic function.
Include the header file, as shown.