On Tuesday, 2 January 2018 at 18:21:13 UTC, Tim Hsu wrote:
I am creating Vector3 structure. I use struct to avoid GC.
However, struct will be copied when passed as parameter to
function
struct Ray {
Vector3f origin;
Vector3f dir;
@nogc @system
this(Vector3f *origin, Vector3f *dir) {
this.origin = *origin;
this.dir = *dir;
}
}
How can I pass struct more efficiently?
Pass the Vector3f by value.
There is not one best solution here: it depends on what you are
doing with the struct, and how large the struct is. It depends on
whether the function will be inlined. It depends on the CPU. And
probably 10 other things.
Vector3f is a small struct (I'm guessing it's 3 floats?), pass it
by value and it will be passed in registers. This "copy" costs
nothing on x86, the CPU will have to load the floats from memory
and store them in a register anyway, before it can write it to
the target Vector3f, regardless of how you pass the Vector3f.
You can play with some code here: https://godbolt.org/g/w56jmA
Passing by pointer (ref is the same) has large downsides and is
certainly not always fastest. For small structs and if copying is
not semantically wrong, just pass by value.
More important: measure what bottlenecks your program has and
optimize there.
- Johan
