[Bug c++/53745] New: Bitshifted value (1 << 31) within enumerator class is calculated incorrectly during compilation.

[Bug c++/53745] New: Bitshifted value (1 << 31) within enumerator class is calculated incorrectly during compilation.

[sbgccbug at yahoo dot co.uk]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53745

             Bug #: 53745
           Summary: Bitshifted value (1 << 31) within enumerator class is
                    calculated incorrectly during compilation.
    Classification: Unclassified
           Product: gcc
           Version: 4.6.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: sbgccbug@yahoo.co.uk


When compiling an 'enum class' (-std=c++0x) that uses bit-shifted values, the
result of "1 << 31" is calculated incorrectly, resulting in -0x80000000
(*negative* 2^31) rather than the correct result of 0x80000000:

// *** BEGIN EXAMPLE CODE (main.cpp) ***

enum class EnumTest : unsigned long int
{
   A = 1 << 30,
   B = 1 << 31
};

int main()
{
   return 0;
}

// *** END EXAMPLE CODE ***

// *** BEGIN gcc-4.6.1 OUTPUT ***

main.cpp|4|error: enumerator value -0x00000000080000000 is too large for
underlying type ‘long unsigned int’|

// *** END gcc-4.6.1 OUTPUT ***

[Bug c++/53745] Bitshifted value (1 << 31) within enumerator class is calculated incorrectly during compilation.

[schwab@linux-m68k.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53745

Andreas Schwab <schwab@linux-m68k.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID

--- Comment #1 from Andreas Schwab <schwab@linux-m68k.org> 2012-06-21 13:35:26 UTC ---
1<<31 is an expression of type int, and overflows when int has 32 bits.  This
is independent of the context of its use.  You should write 1UL<<31 instead.

[Bug c++/53745] Bitshifted value (1 << 31) within enumerator class is calculated incorrectly during compilation.

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53745

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-06-21 13:36:24 UTC ---
The initializer must be converted constant expression of type unsigned long, so
by my reading it's ill-formed because (1<<31) has type int and is negative so
requires a narrowing conversion to unsigned long.

[Bug c++/53745] [C++11] Poor diagnostic for ill-formed narrowing conversion in enumerator initializer

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53745

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
   Last reconfirmed|                            |2012-06-21
         Resolution|INVALID                     |
            Summary|Bitshifted value (1 << 31)  |[C++11] Poor diagnostic for
                   |within enumerator class is  |ill-formed narrowing
                   |calculated incorrectly      |conversion in enumerator
                   |during compilation.         |initializer
     Ever Confirmed|0                           |1

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-06-21 17:51:43 UTC ---
Re-opening since the diagnostic could be better, the value is not "too large",
the problem is with the sign, not the magnitude.

enum E : unsigned long long { e = -1 };

e.cc:1:26: error: enumerator value -1 is too large for underlying type
'unsigned long long'

Clang gives a more accurate diagnostic, though not necessarily more helpful if
you don't know what a narrowing conversion is:

e.cc:1:25: error: enumerator value evaluates to -1, which cannot be narrowed to
type 'unsigned long long' [-Wc++11-narrowing]

[Bug c++/53745] [C++11] Poor diagnostic for ill-formed narrowing conversion in enumerator initializer

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53745

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |vvnic.holas at gmail dot
                   |                            |com

--- Comment #4 from Paolo Carlini <paolo.carlini at oracle dot com> 2013-05-03 23:23:15 UTC ---
*** Bug 57164 has been marked as a duplicate of this bug. ***

[Bug c++/53745] [C++11] Poor diagnostic for ill-formed narrowing conversion in enumerator initializer

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53745

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |ASSIGNED
         AssignedTo|unassigned at gcc dot       |paolo.carlini at oracle dot
                   |gnu.org                     |com

--- Comment #5 from Paolo Carlini <paolo.carlini at oracle dot com> 2013-05-04 13:09:37 UTC ---
I'm going to propose changing the message to "... outside the range...",
similarly to ICC: it seems a good compromise, less misleading than the current
message, less technical than clang's.

[Bug c++/53745] [C++11] Poor diagnostic for ill-formed narrowing conversion in enumerator initializer

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53745

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.9.0

--- Comment #6 from Paolo Carlini <paolo.carlini at oracle dot com> 2013-05-05 00:29:13 UTC ---
Fixed for 4.9.0.