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

//=============================================================================
// Subtraction functions
//=============================================================================

//
// UINT8 subtraction
//
_Must_inspect_result_
__inline
NTSTATUS
RtlUInt8Sub(
    _In_ UINT8 u8Minuend,
    _In_ UINT8 u8Subtrahend,
    _Out_ _Deref_out_range_(==, u8Minuend - u8Subtrahend) UINT8* pu8Result)
{
    NTSTATUS status;

    if (u8Minuend >= u8Subtrahend)
    {
        *pu8Result = (UINT8)(u8Minuend - u8Subtrahend);
        status = STATUS_SUCCESS;
    }
    else
    {
        *pu8Result = UINT8_ERROR;
        status = STATUS_INTEGER_OVERFLOW;
    }

    return status;
}

#endif
#endif
View code on GitHub

// ntintsafe.h

NTSTATUS RtlUInt8Sub(
  [in]  UINT8 u8Minuend,
  [in]  UINT8 u8Subtrahend,
  [out] UINT8 *pu8Result
);
View the official Windows Driver Kit DDI reference

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Windows Driver Kit DDI reference (nf-ntintsafe-rtluint8sub)

RtlUInt8Sub function

Description

The RtlUInt8Sub routine subtracts one value of type UINT8 from another.

Parameters

`u8Minuend` [in]

The value from which u8Subtrahend is subtracted.

`u8Subtrahend` [in]

The value to subtract from u8Minuend.

`pu8Result` [out]

A pointer to the result. 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

RtlUInt8Sub returns STATUS_SUCCESS if the routine is successful. Possible error return values include the following status code.

Return code	Description
STATUS_INTEGER_OVERFLOW	An arithmetic overflow occurred.

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