D arithmetic problem

[davidl]

在 Wed, 03 Jun 2009 15:23:45 +0800，Walter Bright  
<newshound1 at digitalmars.com> 写道:

> Don wrote:
>> I agree, it's bug-prone.
>
> Any two's complement arithmetic system, with types of different sizes  
> and signed-ness, is going to have quirks. It's inescapable. Back when C  
> was standardized in the 80's, there was a huge debate about whether to  
> use signed-preserving rules or value-preserving rules. After much  
> debate, it came down to pick set A of problems or set B of problems. The  
> committee picked one (value preserving) and moved on.
>
> http://books.google.com/books?id=yxLISD0TAbEC&pg=PA35&lpg=PA35&dq=signed+preserving+versus+value+preserving+integral+promotion+rules&source=bl&ots=tCRBjyS4jC&sig=VCVgyAr9u0ItJbcZ5r-fLnxGmX4&hl=en&ei=riMmSufaCafcswO4vbWUBg&sa=X&oi=book_result&ct=result&resnum=9
>
>
>> Ideally, we'd disallow implicit widening casts for signed types in  
>> logical operations. But can that be done without creating too many  
>> language quirks?
>
>
> The problem with changing the rules is that the value preserving rules  
> are now deeply ingrained into how C (and C++) code is written. Changing  
> them would mean that translating complex code from C to D may produce  
> silent changes in behavior. I believe this would be very bad for D  
> because it means people would not be able to translate such code to D.
>
> (After all, it's one thing to translate, say, an encryption program from  
> C to D. It's quite another thing to understand it well enough to be able  
> to debug it, or even verify that it is working correctly.)

I highly whether the code by utilizing this kind of semantic can be called  
well-written. Porting such code to D doesn't make D any better, also it  
requires a lot of effort to port. I don't know any famous C to D or C++ to  
D converter. Instead, I have a working C# to D portting tool which can  
port some specific code by hacking on top of SharpDevelop in only few  
weeks effort. Porting C# code to D might be more attractive.

-- 
使用 Opera 革命性的电子邮件客户程序: http://www.opera.com/mail/