BOOLEAN NlsMbCodePageTag = FALSE; /* exported *///全局导出

NTSTATUS
NTAPI
RtlAnsiStringToUnicodeString(
    IN OUT PUNICODE_STRING UniDest,
    IN PANSI_STRING AnsiSource,
    IN BOOLEAN AllocateDestinationString)
{
    NTSTATUS Status;
    ULONG Length;
    ULONG Index;

    PAGED_CODE_RTL();

    if (NlsMbCodePageTag == FALSE)
    {
        //计算ANSI到UNICODE的长度，这里的Length是有效长度+sizeof(WCHAR)
        Length = AnsiSource->Length * 2 + sizeof(WCHAR);
    }
    else
    {
    	//计算ANSI到UNICODE的长度，这里的Length是有效长度+sizeof(WCHAR)
        Length = RtlxAnsiStringToUnicodeSize(AnsiSource);
    }
    if (Length > MAXUSHORT) //MAXUSHORT = 0xffff
    	return STATUS_INVALID_PARAMETER_2;
    //有效长度
    UniDest->Length = (USHORT)Length - sizeof(WCHAR);

    if (AllocateDestinationString)
    {
    	//如果需要申请内存，那么给目标对象申请
        UniDest->Buffer = RtlpAllocateStringMemory(Length, TAG_USTR);
        UniDest->MaximumLength = (USHORT)Length;
        if (!UniDest->Buffer) return STATUS_NO_MEMORY;
    }
    else if (UniDest->Length >= UniDest->MaximumLength)
    {
        return STATUS_BUFFER_OVERFLOW;
    }

    
    ASSERT(!(UniDest->MaximumLength & 1) && UniDest->Length <= UniDest->MaximumLength);

	//进行转换赋值
    Status = RtlMultiByteToUnicodeN(UniDest->Buffer,
                                    UniDest->Length,
                                    &Index,
                                    AnsiSource->Buffer,
                                    AnsiSource->Length);

    if (!NT_SUCCESS(Status))
    {
        if (AllocateDestinationString)
        {
            RtlpFreeStringMemory(UniDest->Buffer, TAG_USTR);
            UniDest->Buffer = NULL;
        }

        return Status;
    }

    UniDest->Buffer[Index / sizeof(WCHAR)] = UNICODE_NULL;//字符串空字符结尾
    return Status;
}

NTSTATUS NTAPI
RtlMultiByteToUnicodeN(OUT PWCHAR UnicodeString,
                       IN ULONG UnicodeSize,
                       OUT PULONG ResultSize,
                       IN PCSTR MbString,
                       IN ULONG MbSize)
{
    ULONG Size = 0;
    ULONG i;

    PAGED_CODE_RTL();

    if (!NlsMbCodePageTag)
    {
        if (MbSize > (UnicodeSize / sizeof(WCHAR)))
            Size = UnicodeSize / sizeof(WCHAR);
        else
            Size = MbSize;

        if (ResultSize)
            *ResultSize = Size * sizeof(WCHAR);

        for (i = 0; i < Size; i++)
            UnicodeString[i] = NlsAnsiToUnicodeTable[(UCHAR)MbString[i]];
    }
    else
    {
        UCHAR Char;
        USHORT LeadByteInfo;
        PCSTR MbEnd = MbString + MbSize;

        for (i = 0; i < UnicodeSize / sizeof(WCHAR) && MbString < MbEnd; i++)
        {
            Char = *(PUCHAR)MbString++;
			
			//如果是ascii字符值小于128，则直接进行赋值
            if (Char < 0x80)
            {
                *UnicodeString++ = Char;
                continue;
            }
			//NlsLeadByteInfo NlsAnsiToUnicodeTable这些指针都是全局指针
			//在源码中查看直接赋值为NULL，其实这些指针应该都是指向一张转换表
            LeadByteInfo = NlsLeadByteInfo[Char];

            if (!LeadByteInfo)
            {
            	//进行查表转换
                *UnicodeString++ = NlsAnsiToUnicodeTable[Char];
                continue;
            }
			//如果以上两种情况都不存在，那么进行这种转换
            if (MbString < MbEnd)
                *UnicodeString++ = NlsLeadByteInfo[LeadByteInfo + *(PUCHAR)MbString++];
        }

        if (ResultSize)
            *ResultSize = i * sizeof(WCHAR);//返回赋值的ascii字符个数
    }
    return STATUS_SUCCESS;
}