[macstl-dev] Re: Question about sized booleans

[Ilya Lipovsky]

>
>
>> I want to be able to do:
>>
>> v3 = (v1 || v2), where v1 & v2 are valarray<int> and use v3 any way I 
>> want to. Currently, I have problems with that. Declaring v3 as 
>> valarray<int> produces compile-time error (the same goes for 
>> valarray<macstl::boolean<int> >, as mentioned before). Declaring v3 
>> as valarray<bool> produces scalar code. The same goes for operator&& 
>> . What to do... Any suggestions ;) ?
>
>
> Yes I will do that for 0.3.1.


Thanks!

>
>>
>> Also, how to properly use your select function?
>
>
> The signature looks similar to this:
>
> valarray <T> select (const valarray <bool>& boolexpr, const valarray 
> <T>& trueexpr, const valarray <T>& falseexpr);
>
> And it will chunk i.e. optimize using Altivec whenever the boolexpr 
> has the same element size (and in SSE, similar base element) as the 
> trueexpr and falseexpr e.g.
>
> valarray <float> a, b;
> valarray <float> c = select (a < b, a, b);    // is a naive 
> implementation of min (a, b)
>
> You can replace any of the parameters with scalar "constants" (except 
> for all of the constants), so
>
> c = select (true, a, b);
> c = select (a < b, 1.0f, b);
> c = select (a < b, a, 1.0f);
> c = select (true, 1.0f, b);
> c = select (true, a, 1.0f);
> c = select (a < b, 1.0f, 2.0f);
>
> will all work and the constants act as if they are a valarray 
> containing just that constant. (I say "constant" because you can 
> substitute a scalar variable instead but I wanted the examples to be 
> clearer.)

So that means that I was using your "select(...)" correctly. Now I will 
be investigating other venues of resolution. My compiler gives me this:

error: cannot convert `stdext::valarray<float>' to `fd_set*' for 
argument `2' to `int select(int, fd_set*, fd_set*, fd_set*, timeval*)'

even though I don't include any system headers.

-Ilya