The large integer functions and structures originally provided support for 64-bit values on 32-bit Windows. Now, your C compiler may support 64-bit integers natively. For example, Microsoft Visual C++ supports the __int64 sized integer type. For more information, see the documentation included with your C compiler.
For information on 64-bit integers on 64-bit Windows, see The New Data Types.
Large Integer Operations
Applications can multiply signed or unsigned 32-bit integers, generating 64-bit results, by using the Int32x32To64 and UInt32x32To64 functions. Applications can shift bits in 64-bit values to the left or right by using the Int64ShllMod32, Int64ShraMod32, and Int64ShrlMod32 functions. These functions provide logical and arithmetic shifting.
Applications can also multiply and divide 32-bit values in a single operation by using the MulDiv function. Although the result of the operation is a 32-bit value, the function stores the intermediate result as a 64-bit value, so that information is not lost when large 32-bit values are multiplied and divided.
Large Integer Reference