libstdc++/6282: bitset<0> results in nonsense behavior

[pme at gcc dot gnu dot org]

>Number:         6282
>Category:       libstdc++
>Synopsis:       bitset<0> results in nonsense behavior
>Confidential:   no
>Severity:       critical
>Priority:       low
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Apr 12 13:16:00 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     Phil Edwards
>Release:        3.x
>Organization:
>Environment:
All.  (Not platform-specific code.)
>Description:
Creating a std::bitset instance of zero size still stores
a word's worth of data.

Consider

  std::bitset<1>  x(555555);
  int i = x.count();

Only the least significant bit from 555555 will be stored,
and i will correctly be set to 1 (the count of "on" bits
in x).  But if x is defined as

  std::bitset<0>  x(555555);

then there are still sizeof(unsigned long) bits being
stored and initialized, and x.count() returns 9 instead of
the more correct 0.  Other bitset member functions return
likewise silly results.


The base class for bitset is not taking into account the
empty case.
>How-To-Repeat:

>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted: