BufferedFile bug?

[Oskar Linde]

Janice Caron wrote:
> On 06/03/2008, Oskar Linde <oskar.lindeREM at ovegmail.com> wrote:
>>  The problem is that:
>>
>>  uint x = 1;
>>  long y = -x;
>>
>>  yields y == 4294967295
> 
> (I changed the variable names because lowercase L looks like one to me).
> 
> Huh?
> 
> Why doesn't y equal minus one?
> 
> I wouldn't call that a bug in BufferedStream.flush(), I'd call it a
> bug in D's arithmetic generally.

It is hard to classify something as a bug when it behaves exactly as 
specified. See "Usual Arithmetic Conversion" under:

http://www.digitalmars.com/d/1.0/type.html

This is exactly how it works in C too.

> The way I see it, there are two possible fixes:
> 
> (1) Disallow unary minus completely for all unsigned types. Thus

Unary minus is not the only affected operator. All integer arithmetic is 
affected.

> (2), when unary minus is applied to an unsigned type, promote ubyte to
> short, ushort to int, uint to long, ulong to cent (...best make that
> one illegal for now). That would mean
> 
>     uint x = 1;
>     long y = -x; /* OK */
> 
> but
> 
>     uint x = 1;
>     int y = -x; /* Error */
> 
> Either would work, but the status quo /can't/ be right!!!???

There has been some previous discussions along those lines. For example:

http://www.digitalmars.com/d/archives/digitalmars/D/unsigned_policy_47929.html#N47954

Today, all arithmetic operations are promoted to int/uint, and by the 
magic of the 2's-complement representation, things actually work out 
most of the time.

for example:

int a = (rand() % 3) - 1;

works fine, while

double b = (rand() % 3) - 1;

doesn't.

-- 
Oskar