🚀 go-pugleaf

Pablo Halpern (phalpern@truffle.ultranet.com) wrote:
|> I am trying to optimize a template for use with built-in types and
|> pointers. I have a function that moves objects within or between arrays.
|> The first cut is simply:

|>   template <class type>
|>   void List<type>::move_elems(type *dest, const type *src, int numelems)
|>   {
|>     // Copy elements one at a time using type's assignment operator
|>     while (numelems-- > 0)
|>       *dest++ = *src++;
|>   }

|> This will work for any type with a canonical operator=(). However, this
|> is not efficient for built-in types and pointers, which are better
|> copied with the following expression:

|>   memmove(dest, src, sizeof(type) * numelems);

Is this really true?  I was under the impression that on most machines
where it made a significant difference (CISC architectures), the
compilers did this optimization for you.  (Microsoft once had a full
page ad in Byte claiming they did it in their C compiler; as this was a
fairly long time ago, I would imagine that most compilers are doing it
today.  Of course, on a RISC, it probably won't make a significant
difference.)
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James Kanze           (+33) 88 14 49 00          email: kanze@gabi-soft.fr
GABI Software, Sarl., 8 rue des Francs Bourgeois, 67000 Strasbourg, France
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