On Saturday, 30 May 2015 at 13:57:28 UTC, Rikki Cattermole wrote:
On 31/05/2015 1:49 a.m., short2cave wrote:
On Saturday, 30 May 2015 at 12:34:21 UTC, Rikki Cattermole
wrote:
On 30/05/2015 11:46 p.m., short2cave wrote:
Consider this struct:
---
Foo
{
uint a,b,c;
float d,e,f;
}
---
in a collection:
---
Foo[] foos;
---
Looping a particular member is not cache friendly
---
foreach(foo;foos){/*foo.a = ...*/}
---
but to write clear, understable, structured code, the struct
is
necessary.
So, is it possible to imagine an abstraction such as
---
FooData
{
uint[] a,b,c;
float[] d,e,f;
Foo[] items(){}
}
---
that would allow to loop over the data in a cache-friendly
way ?
You think that an item as the member but they are actually
stored using
another memory layout ?
A template for this would be particularly usefull:
template DataFriendlyStruct(T) if (is(T==struct) && isPOD!T)
{
alias DataFriendlyStruct = ...
}
What exactly are you doing that such a micro optimization is
necessary?
It's just that i try to concrectly apply some things read in a
paper a
few monthes ago. I won't be able to find the link again but
the idea is
simple, here is a short summary:
structured types are dead, people gotta stup using classes and
structs. >They're not efficient.
>
That's not a scoop. Programs are slow because of that but
struct and
class allow a complexity in the design that you can't reach
with globals.
The problem if you have global declarations of data everywhere
things
become quickly super heavy, for example:
---
float[] effect1_filter_1_omega;
float[] effect1_filter_2_omega;
float[] effect2_filter_1_omega;
float[] effect2_filter_2_omega;
float[] voice1_osc1_phasemod_source1
float[] voice1_osc2_phasemod_source2
float[] voice2_osc1_phasemod_source1
float[] voice2_osc2_phasemod_source2
---
efficient to loop but imagine that we talking about 8
oscillators, 32
voices per oscillator, 2 effects per voice, etc...
so an abstraction is required to give a
"pseudo-structured-interface".
There is one other cost to mention, the human cost. The cost to
which the developer takes to understand it. That's why I called
it a micro optimisation.
But in this case, it will still depend upon what you are doing.
Food for thought. CPU caches are pretty weird now days. You
can't really predicate what will go into them and when.
So while yes you would put everything into arrays to group the
data. You probably will be relying on an item from one and an
item for another.
So a struct should be a unit of work.
Also allocated the array in one go. Large as possible. It'll
make things a little bit happier.
I can't really talk about much else.
template, man, think template. Once it's done it can be
instantiated at the ∞ with any struct used as model. A library
template, a type cons. Once the template done, it has 0 cost.
