https://issues.dlang.org/show_bug.cgi?id=21151

kinke <kinke@gmx.net> changed:

           What    |Removed                     |Added
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             Status|NEW                         |RESOLVED
                 CC|                            |kinke@gmx.net
         Resolution|---                         |INVALID

--- Comment #1 from kinke <kinke@gmx.net> ---
This is a usual arithmetic conversion, see https://dlang.org/spec/type.html#usual-arithmetic-conversions. C++ does the same, see https://cpp.godbolt.org/z/YGnr44.

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https://issues.dlang.org/show_bug.cgi?id=21151

--- Comment #2 from mw <mingwu@gmail.com> ---
It can NOT silently do this, at least a warning.

BTW, on Windows, dmd correctly output -2500.

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https://issues.dlang.org/show_bug.cgi?id=21151

mw <mingwu@gmail.com> changed:

           What    |Removed                     |Added
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             Status|RESOLVED                    |REOPENED
         Resolution|INVALID                     |---

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https://issues.dlang.org/show_bug.cgi?id=21151

--- Comment #3 from mw <mingwu@gmail.com> ---
Just because C++ did it doesn't means it's correct.

And D supposed to be an improvement of C++.

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https://issues.dlang.org/show_bug.cgi?id=21151

FeepingCreature <default_357-line@yahoo.de> changed:

           What    |Removed                     |Added
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                 CC|                            |default_357-line@yahoo.de

--- Comment #4 from FeepingCreature <default_357-line@yahoo.de> ---
I'm completely on mw's side here, even understanding why D does this. Silently casting negative signed to unsigned violates the foundational principle that at least on built-in types, implicit conversions should never throw away data.

Though I think it should be a spec enhancement issue, to correct 6.8.1.4.4: "The signed type is converted to the unsigned type." https://dlang.org/spec/type.html#usual-arithmetic-conversions

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https://issues.dlang.org/show_bug.cgi?id=21151

Basile-z <b2.temp@gmx.com> changed:

           What    |Removed                     |Added
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                 CC|                            |b2.temp@gmx.com

--- Comment #5 from Basile-z <b2.temp@gmx.com> ---
I agree too that this is a bug but I think it should be closed as WONTFIX, to keep a certain form of recognition.

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https://issues.dlang.org/show_bug.cgi?id=21151

--- Comment #6 from mw <mingwu@gmail.com> ---
OK, let me write this in this way to show it's impact:

==================================
import std.algorithm;
import std.stdio;

void main() {
  long[] a = [-5000, 0];
  long   c = sum(a) / a.length;
  writeln(c);
}
==================================


$ ./divbug
9223372036854773308

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https://issues.dlang.org/show_bug.cgi?id=21151

--- Comment #7 from kinke <kinke@gmx.net> ---
(In reply to mw from comment #2)
> BTW, on Windows, dmd correctly output -2500.

Not on Windows, but for 32-bit targets, as an unsigned 32-bit int is converted to a signed 64-bit long in that case, according to spec 6.8.1.4.3.

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https://issues.dlang.org/show_bug.cgi?id=21151

--- Comment #8 from mw <mingwu@gmail.com> ---
$ /mnt/c/project/dmd2/windows/bin64/dmd.exe --version
DMD64 D Compiler v2.092.0-dirty
Copyright (C) 1999-2020 by The D Language Foundation, All Rights Reserved
written by Walter Bright

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https://issues.dlang.org/show_bug.cgi?id=21151

Basile-z <b2.temp@gmx.com> changed:

           What    |Removed                     |Added
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           Keywords|                            |wrong-code

--- Comment #9 from Basile-z <b2.temp@gmx.com> ---
Werll after the new facts about the behavior on i386 I retire what I said ealier. This should not be closed. Tagged it as "wrong code".

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