Re: Does Casting Slow a Program Down?

"PeterOut" <MajorSetback@xxxxxxxxxx> wrote in message
news:1170255047.573548.183190@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
If I had code like this.

unsigned short usLimit=10
int a[10], i;

for (i=0; i<(int)usLimit; ++i)
{
a[i]=(int)usLimit;
}

would it run slower than this?

int a[10], i, iLimit=10;

for (i=0; i<iLimit; ++i)
{
a[i]=iLimit;
}

It usually depends on the compiler. Compilers vary greatly in the quality
of the optimizations they can perform.

However, in this particular case, the answer would usually be "NO". I have
not seen a compiler so poor that it would treat the two cases you gave
differently.

I would expect more variability in a case like this:

int x,y;
x = 10;
y = (char)x;

A clever compiler will recognize that with x==10, the cast has no effect. A
less clever compiler would actually truncate to a character than convert
back to an int.

In your example, most compilers will realize that the cast has no effect.
("Realize" is an inappropriate anthropomorphization of the compiler -- more
precisely, the expression trees it builds and the algorithms it applies ot
the trees will weed this out.)
--
David T. Ashley (dta@xxxxxxxx)
http://www.e3ft.com (Consulting Home Page)
http://www.dtashley.com (Personal Home Page)
http://gpl.e3ft.com (GPL Publications and Projects)


.

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