#ifndef _NTINTSAFE_H_INCLUDED_
#if WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_APP | WINAPI_PARTITION_SYSTEM | WINAPI_PARTITION_GAMES)

//=============================================================================
// Addition functions
//=============================================================================

//
// UINT8 addition
//
_Must_inspect_result_
__inline
NTSTATUS
RtlUInt8Add(
    _In_ UINT8 u8Augend,
    _In_ UINT8 u8Addend,
    _Out_ _Deref_out_range_(==, u8Augend + u8Addend) UINT8* pu8Result)
{
    NTSTATUS status;

    if (((UINT8)(u8Augend + u8Addend)) >= u8Augend)
    {
        *pu8Result = (UINT8)(u8Augend + u8Addend);
        status = STATUS_SUCCESS;
    }
    else
    {
        *pu8Result = UINT8_ERROR;
        status = STATUS_INTEGER_OVERFLOW;
    }

    return status;
}

#endif
#endif
View code on GitHub

// ntintsafe.h

NTSTATUS RtlUInt8Add(
  [in]  UINT8 u8Augend,
  [in]  UINT8 u8Addend,
  [out] UINT8 *pu8Result
);
View the official Windows Driver Kit DDI reference

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Windows Driver Kit DDI reference (nf-ntintsafe-rtluint8add)

RtlUInt8Add function

Description

Adds two values of type UINT8.

Parameters

`u8Augend` [in]

The first value in the equation.

`u8Addend` [in]

The value to add to u8Augend.

`pu8Result` [out]

A pointer to the sum. If the operation results in a value that overflows or underflows the capacity of the type, the function returns STATUS_INTEGER_OVERFLOW and this parameter is not valid.

Return value

Returns STATUS_SUCCESS if the operation is successful.

See the implementation of this helper function in ntintsafe.h in the WDK for possible error return values.

Remarks

This is one of a set of inline functions designed to provide arithmetic operations and perform validity checks with minimal impact on performance.

View the official Windows Driver Kit DDI reference