RE: [Dev-C++] #DEFINE versus cont variables in array inicializations

[Per W. <pw...@ia...>]

At least for scalar data types, it doesn't matter if a global const xx
variable is used in other modules.

Since the compiler inlines the value of the const variable everytime it is
used, there is no need to keep a global reference for use by other source
files.

Since an address is 4 bytes for normal 32-bit code, any const variable <=
4 byte will consume same space for the inlined value as the address needed
to reference a real variable. However, the inlined value will
automatically follow in the instruction stream, thereby using the L1/L2
caches optimally, while an address reference to a separate storage would
have to use a different cache line in the processor.

The net result is that a global 'const int xx = <value>' is just as
efficient as if the declararation was written locally within a function.
Both alternatives will be inlined, without any global or auto variable
whatsoever.

/Per W

On Fri, 30 May 2003, Ioannis Vranos wrote:

> > -----Original Message-----
> > From: Per Westermark [mailto:pw...@ia...]
> > Sent: Friday, May 30, 2003 2:39 PM
> > To: Ioannis Vranos
> > Cc: Dev-C++ Mailing List
> > Subject: RE: [Dev-C++] #DEFINE versus cont variables in array
> > inicializations
> >
> >
> > If the reference is declared auto, the compiler can optimize away the
> > reference, but if it's declared as a global, the compiler
> > won't optimize
> > it away, since by definition, a reference - just like a
> > pointer - is an
> > address to a value, not the value itself.
>
>
>
> Yes I agree. I was talking about local auto const references. Global const
> variables are difficult to optimise out too, because the compiler doesn't
> know if it is used in another compilation unit (file).
>
>
>
>
> Ioannis Vranos
>
> * Programming pages: http://www.noicys.freeurl.com
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