Ideas from the Chapel language (swap)

[Gregor Richards]

Derek Parnell wrote:
> On Wed, 03 Oct 2007 14:53:57 -0400, Bruce Adams wrote:
> 
>> bearophile Wrote:
>>
>>> The Cray Inc is designing the Chapel Language:
>>> http://chapel.cs.washington.edu/
>>> The following notes are from the specification V. 0.750:
>>> http://chapel.cs.washington.edu/spec-0.750.pdf
>>> I think it's rather cute, it looks like a cross between C++, Fortress and Python. Here are few things I think can be interesting for D designers too:
>>>
>>> - Chap. 11.5 page 65, swap operator (useful but probably not enough to justify a new operator)
>> swap is very useful especially in exception safe programming.
>> I would like to see swap used as the default implementation of D's transfer constructor (and C++0x's forthcoming move constructor)
> 
> Isn't a simple template such this sufficient?
> 
> template swap(TYPE)
> {
>     void swap(ref TYPE a, ref TYPE b)
>     {
>         synchronized
>         {
>           TYPE temp = a;
>           a = b;
>           b = temp;
>         }
>     }
> 
> }
> 
> 

For the ridiculously-insane:

void swap(T)(ref T a, ref T b)
{
     synchronized {
         // this should be some kind of static for ...
         for (size_t i = 0; i < (a.sizeof/size_t.sizeof); i++) {
             (cast(size_t*) &a)[i] ^= (cast(size_t*) &b)[i];
             (cast(size_t*) &b)[i] = (cast(size_t*) &a)[i] ^ 
(cast(size_t*) &b)[i];
             (cast(size_t*) &a)[i] ^= (cast(size_t*) &b)[i];
         }
     }
}

Add some loop unrolling and that's more efficient than memcpy :P

  - Gregor Richards

PS: /me <3 XOR swapping