#ifndef _NTINTSAFE_H_INCLUDED_
#if WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_APP | WINAPI_PARTITION_SYSTEM | WINAPI_PARTITION_GAMES)
/////////////////////////////////////////////////////////////////////////
//
// signed operations
//
// Strongly consider using unsigned numbers.
//
// Signed numbers are often used where unsigned numbers should be used.
// For example file sizes and array indices should always be unsigned.
// (File sizes should be 64bit integers; array indices should be size_t.)
// Subtracting a larger positive signed number from a smaller positive
// signed number with RtlIntSub will succeed, producing a negative number,
// that then must not be used as an array index (but can occasionally be
// used as a pointer index.) Similarly for adding a larger magnitude
// negative number to a smaller magnitude positive number.
//
// intsafe.h does not protect you from such errors. It tells you if your
// integer operations overflowed, not if you are doing the right thing
// with your non-overflowed integers.
//
// Likewise you can overflow a buffer with a non-overflowed unsigned index.
//
#if defined(ENABLE_INTSAFE_SIGNED_FUNCTIONS)
//
// ptrdiff_t Addition
//
#ifdef _WIN64

#define RtlPtrdiffTAdd RtlLongLongAdd

#endif
#endif
#endif
#endif
View code on GitHub

#ifndef _NTINTSAFE_H_INCLUDED_
#if WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_APP | WINAPI_PARTITION_SYSTEM | WINAPI_PARTITION_GAMES)
/////////////////////////////////////////////////////////////////////////
//
// signed operations
//
// Strongly consider using unsigned numbers.
//
// Signed numbers are often used where unsigned numbers should be used.
// For example file sizes and array indices should always be unsigned.
// (File sizes should be 64bit integers; array indices should be size_t.)
// Subtracting a larger positive signed number from a smaller positive
// signed number with RtlIntSub will succeed, producing a negative number,
// that then must not be used as an array index (but can occasionally be
// used as a pointer index.) Similarly for adding a larger magnitude
// negative number to a smaller magnitude positive number.
//
// intsafe.h does not protect you from such errors. It tells you if your
// integer operations overflowed, not if you are doing the right thing
// with your non-overflowed integers.
//
// Likewise you can overflow a buffer with a non-overflowed unsigned index.
//
#if defined(ENABLE_INTSAFE_SIGNED_FUNCTIONS)
//
// ptrdiff_t Addition
//
#ifdef _WIN64
// ...
#else

_Must_inspect_result_
__inline
NTSTATUS
RtlPtrdiffTAdd(
    _In_ ptrdiff_t Augend,
    _In_ ptrdiff_t Addend,
    _Out_ _Deref_out_range_(==, Augend + Addend) ptrdiff_t* pResult
    )
{
    C_ASSERT(sizeof(LONGLONG) > sizeof(ptrdiff_t));
    return RtlLongLongToPtrdiffT(((LONGLONG)Augend) + ((LONGLONG)Addend), pResult);
}

#endif
#endif
#endif
#endif
View code on GitHub

// ntintsafe.h

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

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

RtlPtrdiffTAdd function

Description

Adds two values of type PTRDIFF_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