Re: sizeof bool > sizeof int ?!?

[Jeroen Dobbelaere <Jeroen dot Dobbelaere at tvd dot be>]

Hi,

I once made a benchmark comparison of several compilers using bench++
for an embedded environment (MPC860).

One of the tests uses an array of bools. gcc (gnupro-97r1) suffered
a lot of the fact that it uses 4 bytes for a bool, compared to
the diab compiler which uses only one byte... (I don't have the values
any more since i moved to another company :( )
(another problem was, that this array was put on the stack so that the stack 
became very large)

Mike Stump wrote:
> 
> > Date: Thu, 20 Aug 1998 12:04:47 -0400
> > From: Richard Hadsell <hadsell@blueskystudios.com>
> > To: EGCS mailing list <egcs@cygnus.com>
> 
> > Richard Hadsell wrote:
> > >
> > > > I realize that some (all?) alpha processors do not handle 1-byte data
> > > > efficiently.  I hope that the situation will change with future
> > > > versions.  But it's hard to believe that alphas don't have an efficient
> > > > instruction set for (4-byte) int data.  What about short data?  Are they
> > > > handled as badly as 1-byte data?
> > > >
> > > > I would prefer that bool be implemented with the best performance in
> > > > mind, including the effects of using memory efficiently, too.
> > >
> > > I haven't seen any comments from the compiler group on their decision to
> > > implement bool as an 8-byte datum on alphas.  If the performance is so
> > > much better that it is worth the cost in memory usage, why is an int
> > > only 4 bytes.  Since the standard allows it to be as big as a long, why
> > > not?  I thought that we could expect an int to be whatever size gives
> > > the best integer performance.
> > >
> > > So I don't understand why a bool is any longer than an int.  What other
> > > considerations were there in making the decision?
> 
> > Comments anyone ?
> 
> No.  Well, ok, I wasn't going to comment, but let me make one meta
> comment about this.  The most persuasive comment is one from a
> benchmark type person that measures the performance in a couple of
> different and realistic ways and makes a statement about the
> performance characteristics, the rest of us can sit back and debate if
> we want to blow the 5%, and save the space, and maybe be better to the
> cache.
> 
> Random comments from random people that say `wow, man, 8 bytes instead
> of one bit, sounds like a bug' is less interesting to me.