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

//
// size_t addition
//
_Must_inspect_result_
__inline
NTSTATUS
RtlSizeTAdd(
    _In_ size_t Augend,
    _In_ size_t Addend,
    _Out_ _Deref_out_range_(==, Augend + Addend) size_t* pResult)
{
    NTSTATUS status;

    if ((Augend + Addend) >= Augend)
    {
        *pResult = (Augend + Addend);
        status = STATUS_SUCCESS;
    }
    else
    {
        *pResult = SIZE_T_ERROR;
        status = STATUS_INTEGER_OVERFLOW;
    }

    return status;
}

#endif
#endif
View code on GitHub

// ntintsafe.h

NTSTATUS RtlSizeTAdd(
  [in]  size_t Augend,
  [in]  size_t Addend,
  [out] size_t *pResult
);
View the official Windows Driver Kit DDI reference

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

RtlSizeTAdd function

Description

Adds two values of type SIZE_T.

Parameters

`Augend` [in]

The first value in the equation.

`Addend` [in]

The value to add to Augend.

`pResult` [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