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

//
// USHORT -> UCHAR conversion
//
_Must_inspect_result_
__inline
NTSTATUS
RtlUShortToUChar(
    _In_ USHORT usOperand,
    _Out_ _Deref_out_range_(==, usOperand) UCHAR* pch)
{
    NTSTATUS status;

    if (usOperand <= 255)
    {
        *pch = (UCHAR)usOperand;
        status = STATUS_SUCCESS;
    }
    else
    {
        *pch = '\0';
        status = STATUS_INTEGER_OVERFLOW;
    }

    return status;
}

#endif
#endif
View code on GitHub

// ntintsafe.h

NTSTATUS RtlUShortToUChar(
  [in]  USHORT usOperand,
  [out] UCHAR  *pch
);
View the official Windows Driver Kit DDI reference

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

RtlUShortToUChar function

Description

Converts a value of type USHORT to a value of type UCHAR.

Parameters

`usOperand` [in]

The value to be converted.

`pch` [out]

A pointer to the converted value. In the case where the conversion causes a truncation of the original value, 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 type conversions and perform validity checks with minimal impact on performance.

View the official Windows Driver Kit DDI reference