[cfe-dev] Inconsistent types used to represent bitwidth

[Hartmut Kaiser]

Cedric,

> >> > IIUC, the bitwidth is most of the time the number of 
> bits needed to 
> >> > represent the size, i.e. 32 for uint32_t. In this case 64 is the 
> >> > largest number these kind of variables will ever hold, no?
> >>
> >> Yes, except that what is the size of "uint32_t[100000000000LL]" ?
> >
> >    sizeof(uint32_t[100000000000LL]) < 2^64,
> >
> > so the size is representable with 64 bits, which means the 
> > corresponding bitwidth is not even '64', which conveniently 
> fits into a int8_t.
> >
> > But probably I'm getting something really wrong here.
> > Regards Hartmut
> 
> I think we lost the correct definition of bitwith along the way.  
> quoting earlier post from this thread:
> 
> > >>> recognized, that the bitwith (size of a type in bits) is
> 
> for me, bitwith( X ) == 8*sizeof( X )

If bitwidth is 8*sizeof(X), then you're right and I apologize for the
confusion.

> If we speak of the same things, this was done in order to 
> thread the size of bitfield member in an uniform manner with 
> other 'normal'  
> variable.

Hmmm. Obviously I'm lost here or I'm mixing something up. (Please disregard
my statement you quoted above if it increases the confusion)
The point is, that if I'm looking at

clang/Basic/TargetInfo.h:+140:

  /// getLongInfo - Return the size of 'signed long' and 'unsigned long' for
  /// this target, in bits.  
  void getLongInfo(uint64_t &Size, unsigned &Align, SourceLocation Loc) {
    Size = Align = 32;  // FIXME: implement correctly: wrong for
ppc64/x86-64
  }

  /// getLongLongInfo - Return the size of 'signed long long' and
  /// 'unsigned long long' for this target, in bits.  
  void getLongLongInfo(uint64_t &Size, unsigned &Align, 
                            SourceLocation Loc) {
    Size = Align = 64; // FIXME: implement correctly.
  }

we use uint64_t for storing numbers which will have the max value of '64',
no? 

Does this mean we need 64 bits to represent the _size_ of the variable or
does this mean we need 64 bits to represent the variable itself? 

And sorry again for the noise.
Regards Hartmut