On 20 February 2013 02:03, bearophile <bearophileHUGS@lycos.com> wrote:

Don:

Simd comparison generally doesn't return a bool, it returns a bool array,
one per element.

Does (arr[] < 10) mean "is every element in arr less than 10" OR "is any element of arr less than 10" OR "create a bool array which is true for each element which is less than 10" ?

All make sense. That's the problem.

Right, it's a design problem.
I think the right thing to do is to take a look at what's an efficient operation to do in hardware (and then look at what's the most commonly useful operation for users). I think the right design here is to return a bool[N].
So in this case monarch_dodra has to add some more code to test all/any.

Bye,
bearophile

Don is on the money.

I drafted: bool allEqual(a,b)/anyEqual(a,b) and friends in std.simd, but I haven't written them yet (been awol for a while). They're actually quite tricky to get right+fast in a portable way.

all/any comparisons are often used in a boolean way, but they may not be super fast on some architectures. If you want to do component-wise logic, the typical approach is to use component-wise selection, eg:

uint4 mask = compareGreater(a, b); // <- build a bit mask of 0's (false) or 1's (true) where components of a are greater than b.

auto result = select(mask, c, d); // <- select components from c or d according to the bit mask.