RE: [Dev-C++] Use of const qualifier

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

Sorry, no correct answer on that one :-(

Depends on compiler, processor and what the calling function did. If only
targeted for a very specific machine, you have to time execution with the
two alternatives, else leave the function as it is.

Without relying on assembler - which is definitely CPU-specific - you
can't force static variables to be placed at an optimum alignment, and you
can't align the auto variables on the stack.

The auto is probably the best all-around alternative, since it allows the
compiler to use floating point registers. A static variable implies the
survival of the value to the next call, which will probably reduce the
effectivity of the compiler optimization step.

/Per W

On Fri, 1 Nov 2002, Scott Williams wrote:

> Thanks for the reply--very helpful.  You might know the answer to a related
> question. . .
> 
> I have a math-intensive subroutine that is called millions of times (yes,
> millions) by a numerical algorithm.  Currently, all of the variables in this
> subroutine are of automatic extent.  Would there be any efficiency gained by
> instead giving them static extent?  Each call to the subroutine is
> independent so retaining values across calls is not an issue.  Rather, this
> is a question of how the memory access itself is handled.
> 
> Thanks.
> Scott
> 
> 
> -----Original Message-----
> From: Abhijit Shylanath [mailto:mu...@gm...]
> Sent: Thursday, October 31, 2002 5:30 PM
> To: se...@al...; Dev-C++ Mailing List
> Subject: Re: [Dev-C++] Use of const qualifier
> 
> 
> > where myfunc uses the values of x and the array members of y but doesn't
> > change them.  Is there then an efficiency (speed) to be gained by instead
> > declaring:
> >
> > double myfunc(const double x, const double *y)?
> 
> More than speed, the const qualifier is for debugging. It prevents the
> programmer from inadvertently changing the values of certain variables. Some
> new optimizing compilers also use it to align memory more efficiently.
> 
> ___________________________________________________________
> 
> Abhijit Shylanath
> 
> E-mail:   mu...@gm... || ibr...@bi...
> Web-site: http://mudeth.tripod.com/
> 
> 
> 
> 
> 
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