Have you converted it by c2nim initially?
I have no idea about your goal of course -- low level code is still low level
even when coded in low level Nim...
First a remark about your proc
proc `toref`[T](x: var T): ref T =
cast[ref typeof(x)](x.addr)
Run
that can not really work, you can not cast an arbitrary variable of type T to a
ref. In Nim a ref is a GC traced reference to an object, there is a refcount
and type information involved, which is much more than a plain pointer. So
delete this proc now!
Have you verified size of
type
tnode_t* = object
nodetype*: int32
normal*: array[3, float32]
dist*: float32
children*: array[2, int32]
pad*: int32
Run
I am not sure, but I would guess that when you not mark this object with pure
pragma, then there may be additional type information included in the object
instance -- making it larger and decreasing number of instances in cache.
I can't see other issues on a first look, you may have to compare line by line.
Maybe inspect Nim's intermediate C code. Tiny differences may make big
differences in performance, for example the original C code may be optimized
that the C compiler generates fine SIMD instructions, which may not work with
Nim's C output.
But of course it is great that your Nim version works at all!
