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digitalmars.D.bugs - [Issue 7834] New: Assign x%int to int without cast?

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=7834

           Summary: Assign x%int to int without cast?
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: bearophile_hugs eml.cc


--- Comment #0 from bearophile_hugs eml.cc 2012-04-05 17:35:56 PDT ---
In DMD 2.059beta this code compiles with no warnings or errors:


void main(string[] args) {
    uint x;
    ubyte y = cast(ubyte)args.length;
    ubyte z = x % y;
}


So I'd like code similar to this too to compile with no need of a cast:


void main() {
    ulong x;
    int y;
    int z = x % y;
}


Currently it gives:
test.d(4): Error: cannot implicitly convert expression (x % cast(ulong)y) of
type ulong to int

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Apr 05 2012
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=7834


bearophile_hugs eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Assign x%int to int without |Assign x%int to int without
                   |cast?                       |cast
           Severity|enhancement                 |normal


--- Comment #1 from bearophile_hugs eml.cc 2012-04-11 16:02:44 PDT ---
Now I think this is supposed to work, so it's not an enhancement request.

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Apr 11 2012
prev sibling next sibling parent d-bugmail puremagic.com writes:
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SomeDude <lovelydear mailmetrash.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |lovelydear mailmetrash.com


--- Comment #2 from SomeDude <lovelydear mailmetrash.com> 2012-04-21 10:25:02
PDT ---
(In reply to comment #1)

 Now I think this is supposed to work, so it's not an enhancement request.


I don't see where in the spec ulong can be promoted to int.
http://dlang.org/type.html

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Apr 21 2012
prev sibling next sibling parent d-bugmail puremagic.com writes:
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--- Comment #3 from bearophile_hugs eml.cc 2012-04-22 03:35:15 PDT ---
(In reply to comment #2)

 (In reply to comment #1)

 Now I think this is supposed to work, so it's not an enhancement request.


 
 I don't see where in the spec ulong can be promoted to int.
 http://dlang.org/type.html


Thank you, then I think the spec too need to be fixed.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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--- Comment #4 from SomeDude <lovelydear mailmetrash.com> 2012-04-22 10:43:27
PDT ---
That doesn't make any sense. You can't promote a 64 bit unsigned type into a 32
bit signed type.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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--- Comment #5 from bearophile_hugs eml.cc 2012-04-22 11:57:20 PDT ---
(In reply to comment #4)

 That doesn't make any sense. You can't promote a 64 bit unsigned type into a 32
 bit signed type.


Give me some time to think some more about it, I have a backlog of bugs to take
a look at (thanks to your recent efforts).

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Apr 22 2012
prev sibling next sibling parent d-bugmail puremagic.com writes:
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Don <clugdbug yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |clugdbug yahoo.com.au
         Resolution|                            |INVALID


--- Comment #6 from Don <clugdbug yahoo.com.au> 2012-04-23 03:23:44 PDT ---
(In reply to comment #0)

 In DMD 2.059beta this code compiles with no warnings or errors:
 void main(string[] args) {
     uint x;
     ubyte y = cast(ubyte)args.length;
     ubyte z = x % y;
 }



 So I'd like code similar to this too to compile with no need of a cast:
 void main() {
     ulong x;
     int y;
     int z = x % y;
 }


These two bits of code aren't analogous.
If y was -1, when cast to ulong it becomes 0xFFFF_FFFF_FFFF_FFFF
Therefore, x % y could be 0.. ulong.max; there's no way that can fit into an
int.
The compiler is correct.

OTOH if you change int -> uint, it works.

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Apr 23 2012
prev sibling parent d-bugmail puremagic.com writes:
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--- Comment #7 from bearophile_hugs eml.cc 2012-04-24 19:39:48 PDT ---
(In reply to comment #6)


 These two bits of code aren't analogous.
 If y was -1, when cast to ulong it becomes 0xFFFF_FFFF_FFFF_FFFF
 Therefore, x % y could be 0.. ulong.max; there's no way that can fit into an
 int.
 The compiler is correct.


You are of course right, thank you Don and sorry SomeDude.



 OTOH if you change int -> uint, it works.



Right, this compiles:

void main() {
    ulong x;
    uint y = 1;
    int z = x % y;
}

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