http://d.puremagic.com/issues/show_bug.cgi?id=8666

           Summary: std.math.abs(int.min) returns int.min
           Product: D
           Version: D2
          Platform: x86_64
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Phobos
        AssignedTo: nobody@puremagic.com
        ReportedBy: iteronvexor@gmail.com


--- Comment #0 from Caligo <iteronvexor@gmail.com> 2012-09-15 22:02:34 PDT ---
pragma(msg, abs(int.min));

prints:
-2147483648

pragma(msg, abs(cast(long)int.min));

prints:
2147483648L

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Andrei Alexandrescu <andrei@metalanguage.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |andrei@metalanguage.com


--- Comment #1 from Andrei Alexandrescu <andrei@metalanguage.com> 2012-09-16 03:41:26 PDT ---
This is a known anomaly. I assume you are proposing that returning long is the right way to go about it, but it really isn't.

One possibility would be to return uint for int and smaller, and ulong for long. That would be a principled way to go about it, but would break existing code in rather subtle ways.

We could add uabs to return an unsigned type.

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--- Comment #2 from Caligo <iteronvexor@gmail.com> 2012-09-16 10:53:57 PDT ---
(In reply to comment #1)
> This is a known anomaly. I assume you are proposing that returning long is the right way to go about it, but it really isn't.
> 
> One possibility would be to return uint for int and smaller, and ulong for long. That would be a principled way to go about it, but would break existing code in rather subtle ways.
> 
> We could add uabs to return an unsigned type.

No, I wasn't trying to propose that returning a long is the solution.  I was simply trying to demonstrate that the bug isn't triggered when the int is converted to a long.  When I reported this, the anomaly wasn't obvious to me, and I thought there was a bug in math.abs.

In my code I had a template:

template Fun(long a) {
  enum b = abs(a);
  //...
}

but I was instantiating it with Fun!(int.min).  Things started to go wrong when I changed the template to:

template Fun(int a) {
  enum b = abs(a);
  //...
}

In this case the int was being implicitly converted to a long.  I don't think the problem has a solution, but D's contracts will really help those who aren't aware of the anomaly:

Num abs(Num)(Num x)
out(result) {
  assert(result >= 0, "...and a helpful message.");
} body {
  // ...
}

What do you guys think?

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