Thread overview
[Issue 550] New: Shifting by more bits than size of quantity is allowed
Nov 18, 2006
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Nov 18, 2006
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Dec 03, 2006
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May 12, 2007
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Oct 05, 2007
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Oct 20, 2007
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November 18, 2006
http://d.puremagic.com/issues/show_bug.cgi?id=550

           Summary: Shifting by more bits than size of quantity is allowed
           Product: D
           Version: 0.174
          Platform: PC
               URL: http://www.digitalmars.com/d/expression.html
        OS/Version: Windows
            Status: NEW
          Keywords: spec
          Severity: normal
          Priority: P4
         Component: DMD
        AssignedTo: bugzilla@digitalmars.com
        ReportedBy: deewiant@gmail.com
OtherBugsDependingO 511
             nThis:


The compiler allows the following code, directly from the spec:

int c;
c << 33;        // error

Even though "[i]t's illegal to shift by more bits than the size of the quantity being shifted". I'm not sure if this is a useful restriction, but either the spec or DMD is in error.


-- 

November 18, 2006
http://d.puremagic.com/issues/show_bug.cgi?id=550


smjg@iname.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |smjg@iname.com
           Keywords|                            |accepts-invalid




------- Comment #1 from smjg@iname.com  2006-11-18 07:02 -------
If the right operand is a variable, it probably makes more sense from an efficiency POV to allow it.  If it's a compile-time constant, the compiler could easily catch the error.  However, I'm beginning to think such a restriction may interfere with generic programming.


-- 

December 03, 2006
http://d.puremagic.com/issues/show_bug.cgi?id=550


deewiant@gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P4                          |P3




------- Comment #2 from deewiant@gmail.com  2006-12-03 03:36 -------
Only partially fixed in DMD 0.176. Stepping up the priority since compiler behaviour is now inconsistent.

void main() {
        int c;
        c = c << 33; // Error: shift left by 33 exceeds 32
}

void main() {
        int c;
        c = c >> 33; // Works, shouldn't
}

void main() {
        int c;
        c <<= 33; // Works, shouldn't
}

void main() {
        int c;
        c >>= 33; // Works, shouldn't
}

void main() {
        int c;
        c = c >>> 33; // Works, shouldn't
}

void main() {
        int c;
        c >>>= 33; // Works, shouldn't
}

Also, this error message seems a bit strange:

void main() {
        int c;
        c = c << -1; // Error: shift left by -1 exceeds 32
}


-- 

May 12, 2007
http://d.puremagic.com/issues/show_bug.cgi?id=550





------- Comment #3 from deewiant@gmail.com  2007-05-12 03:04 -------
Though the spec doesn't say it, it might as well be worth also disallowing shifts equal to the size of the quantity, as they just zero the value.

Or, at least, they should: some appear to be no-ops currently. As pointed out
by Thomas Kühne in digitalmars.D.learn (
http://lists.puremagic.com/pipermail/digitalmars-d-learn/2007-May/005040.html
), compile-time shifts should be done by ((shift >= x.sizeof * 8) ? 0 : shift)
instead of the current (shift % (x.sizeof * 8)).


-- 

October 05, 2007
http://d.puremagic.com/issues/show_bug.cgi?id=550


matti.niemenmaa+dbugzilla@iki.fi changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic




------- Comment #4 from matti.niemenmaa+dbugzilla@iki.fi  2007-10-05 14:29 -------
DMD 1.022 fixes the issues, but the error messages for the shift expressions
(e.g. c = c << 33) don't have file and line number info. The assignments (c <<=
33) do, though.


-- 

October 20, 2007
http://d.puremagic.com/issues/show_bug.cgi?id=550


braddr@puremagic.com changed:

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




------- Comment #5 from braddr@puremagic.com  2007-10-20 03:05 -------
Per Walter's request, moving the new problem (missing line numbers) into a new bug.  This one has been addressed.  A little counter intuitively, the source of the two issues is probably not actually related to the same part of the code.


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