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digitalmars.D.bugs - [Issue 293] New: Expression uint.max + 1 yields 0 (zero)

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=293

           Summary: Expression uint.max + 1 yields 0 (zero)
           Product: D
           Version: 0.164
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla digitalmars.com
        ReportedBy: m.faustino gmail.com


The expression uint.max + 1, yields 0 (zero). For example, the following code
will print "4294967296 == 0":

//----------------------------------------------------------
import std.stdio;

void main()
{
        ulong u = uint.max;
        writefln(u + 1, " == ", uint.max + 1);

}
//----------------------------------------------------------


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Aug 17 2006
next sibling parent reply Oskar Linde <oskar.lindeREM OVEgmail.com> writes:
d-bugmail puremagic.com wrote:

 http://d.puremagic.com/issues/show_bug.cgi?id=293
 
            Summary: Expression uint.max + 1 yields 0 (zero)
            Product: D
            Version: 0.164
           Platform: PC
         OS/Version: Linux
             Status: NEW
           Severity: normal
           Priority: P2
          Component: DMD
         AssignedTo: bugzilla digitalmars.com
         ReportedBy: m.faustino gmail.com
 
 
 The expression uint.max + 1, yields 0 (zero). For example, the following code
 will print "4294967296 == 0":
 
 //----------------------------------------------------------
 import std.stdio;
 
 void main()
 {
         ulong u = uint.max;
         writefln(u + 1, " == ", uint.max + 1);
 
 }
 //----------------------------------------------------------


This is not a bug. Look under Integer Promotions on 
http://www.digitalmars.com/d/type.html

type type of (uint) + (int) is (uint), not (ulong)

/Oskar
Aug 17 2006
parent BCS <BCS pathlink.com> writes:
Oskar Linde wrote:

 d-bugmail puremagic.com wrote:
 

 http://d.puremagic.com/issues/show_bug.cgi?id=293

            Summary: Expression uint.max + 1 yields 0 (zero)
            Product: D
            Version: 0.164
           Platform: PC
         OS/Version: Linux
             Status: NEW
           Severity: normal
           Priority: P2
          Component: DMD
         AssignedTo: bugzilla digitalmars.com
         ReportedBy: m.faustino gmail.com


 The expression uint.max + 1, yields 0 (zero). For example, the 
 following code
 will print "4294967296 == 0":

 //----------------------------------------------------------
 import std.stdio;

 void main()
 {
         ulong u = uint.max;
         writefln(u + 1, " == ", uint.max + 1);

 }
 //----------------------------------------------------------


 
 
 This is not a bug. Look under Integer Promotions on 
 http://www.digitalmars.com/d/type.html
 
 type type of (uint) + (int) is (uint), not (ulong)
 
 /Oskar


Shouldn't the bug be the overflow in the constant folding? I would hope 
that the DMD would error on overflows in constant expressions.
Aug 17 2006
prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=293


bugzilla digitalmars.com changed:

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





That's how fixed precision integer arithmetic works when it overflows. Not a
bug.


--
Aug 17 2006
prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=293








 That's how fixed precision integer arithmetic works when it overflows. Not a
 bug.
 


So why (u + 1) doesn't overflow when (uint.max + 1) does?
In the code I wrote, aren't those two expressions semantically equivalent?


--
Aug 17 2006
prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=293






u+1 adds 1 to a ulong, which does not overflow because it's a 64 bit type which
is large enough to represent 4294967296. uint.max+1 is a uint, which does
overflow because it's a 32 bit type and not large enough to hold 4294967296.

The expressions are not semantically equivalent.


--
Aug 17 2006
prev sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=293






Ok, thanks. Sorry for the false bug report though.


--
Aug 17 2006