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[Issue 259] Comparing signed to unsigned does not generate an error
Nov 06, 2014
Marc Schütz
Mar 18, 2015
Lionello Lunesu
Apr 17, 2015
Lionello Lunesu
Apr 17, 2015
Stewart Gordon
Jun 04, 2015
naptime
Mar 17, 2016
Sobirari Muhomori
Apr 20, 2016
Jon Degenhardt
2 days ago
Nick Treleaven
May 22, 2014
https://issues.dlang.org/show_bug.cgi?id=259

--- Comment #55 from github-bugzilla@puremagic.com ---
Commit pushed to master at https://github.com/D-Programming-Language/druntime

https://github.com/D-Programming-Language/druntime/commit/8890678458e775e93ade1de307a417b06032ee0f Merge pull request #799 from lionello/bug259

Fixed some signed/unsigned warnings in druntime

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November 06, 2014
https://issues.dlang.org/show_bug.cgi?id=259

Marc Schütz <schuetzm@gmx.net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |schuetzm@gmx.net

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March 15, 2015
https://issues.dlang.org/show_bug.cgi?id=259

--- Comment #56 from Andrei Alexandrescu <andrei@erdani.com> ---
What's left to do about this?

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March 18, 2015
https://issues.dlang.org/show_bug.cgi?id=259

--- Comment #57 from Lionello Lunesu <lio+bugzilla@lunesu.com> ---
(In reply to Andrei Alexandrescu from comment #56)
> What's left to do about this?

I need to finish some of the static code analysis that I have been adding so we get less false positives. It's the false positives that will turn Walter (and others) off and prevent merging it in.

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April 17, 2015
https://issues.dlang.org/show_bug.cgi?id=259

Dominikus Dittes Scherkl <dominikus@scherkl.de> changed:

           What    |Removed                     |Added
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                 CC|                            |dominikus@scherkl.de

--- Comment #58 from Dominikus Dittes Scherkl <dominikus@scherkl.de> ---
The problem is still there, and the behaviour is completely inconsistent, so braking any code isn't a problem I think because I cannot imagine that anybody really relies on the strange behaviour:

unittest
{
    byte   a = -3;
    ubyte  b =  2;
    short  c = -3;
    ushort d =  2;
    int    e = -3;
    uint   f =  2;
    long   g = -3;
    ulong  h =  2;

    assert(a < b);
    assert(c < d);
    assert(e < f); // fails!!
    assert(g < h); // fails!!
    assert(a < h); // fails!!
    assert(b > g);
    assert(d > e);
}

So why don't we change to something that simply always works?

int opCmp(T, U)(const(T) a, const(U) b) pure @safe @nogc nothrow
   if(is(Unqual!T == Unqual!U) || isFloatingPoint!T || isFloatingPoint!U)
{
   // Should be buildin. Naive implementation:
   return a <= b ? a != b ? -1 : 0 : 1;
}

/// Returns negative value if a < b, 0 if they are equal or positive value if a
> b.
/// This will always yield a correct result, no matter which integral types are
compared.
/// It uses one extra comparison operation if and only if
/// one type is signed and the other unsigned but has bigger max.
int opCmp(T, U)(const(T) a, const(U) b) pure @safe @nogc nothrow
   if(isIntegral!T && isIntegral!U && !is(Unqual!T == Unqual!U))
{
   static if(T.sizeof == U.sizeof) alias C = Unsigned!T;
   else alias C = CommonType!(T, U); // this will be the larger type

   static if(isSigned!T && isUnsigned!U && T.sizeof <= U.sizeof)
   {
      return (a < 0) ? -1 : opCmp(cast(Unsigned!C)a, cast(C)b);
   }
   else static if(isUnsigned!T && isSigned!U && T.sizeof >= U.sizeof)
   {
      return (b < 0) ? 1 : opCmp(cast(C)a, cast(Unsigned!C)b);
   }
   else
   {
      // both signed or both unsigned or the unsigned type is smaller
      // and can therefore be safely cast to the signed type
      return opCmp(cast(C)a, cast(C)b);
   }
}

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April 17, 2015
https://issues.dlang.org/show_bug.cgi?id=259

--- Comment #59 from Lionello Lunesu <lio+bugzilla@lunesu.com> ---
It's currently using the C integer promotion rules, which are consistent (they're rules after all) but far from simple.

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April 17, 2015
https://issues.dlang.org/show_bug.cgi?id=259

--- Comment #60 from Dominikus Dittes Scherkl <dominikus@scherkl.de> ---
(In reply to Lionello Lunesu from comment #59)
> It's currently using the C integer promotion rules, which are consistent (they're rules after all) but far from simple.

Ah, ok. I see why a<b and c<d work - they are all promoted to int.
But never the less: who would be affected by changing the behaviour for int and
long? Is really anybody relying on that? And sure that was not a bug from the
beginning?
I don't think that we really should keep bugs just to be consistend with C.
--> this is a case where a compiler warning is good: "Comparing signed with
unsigned values. This works in D but may be a performance issue and behaves
different from C. Is this intended?" (of course works only after the fix :-)

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April 17, 2015
https://issues.dlang.org/show_bug.cgi?id=259

--- Comment #61 from Stewart Gordon <smjg@iname.com> ---
(In reply to Dominikus Dittes Scherkl from comment #58)
> The problem is still there, and the behaviour is completely inconsistent, so braking any code isn't a problem I think because I cannot imagine that anybody really relies on the strange behaviour:

Exactly, because it won't break any code.  It will cause code that is already broken to correctly error.

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June 04, 2015
https://issues.dlang.org/show_bug.cgi?id=259

naptime <naptimeentertainment@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |naptimeentertainment@gmail.
                   |                            |com

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June 09, 2015
https://issues.dlang.org/show_bug.cgi?id=259

Andrei Alexandrescu <andrei@erdani.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|2.059                       |---
            Version|D1 & D2                     |D2

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