I have some C functions that perform fast operations on lists of numbers.
Until now, I transfer Tcl data in the shape of lists to those C functions.
In some cases the Tcl data is stored in dictionaries so I run some Tcl loops over the Tcl dict, put the needed data into lists and finally pass the lists to the C function.
Since performance is paramount, I'm thinking that the above method might not be the fastest.
If I would directly pass the Tcl dict to the C function, would that be faster?
What if the Tcl dict is "nested" so there are multiple keys that lead to a value?
Can I (efficiently) access nested dicts with the C API?
The examples found on the Wiki and Help are always about simple (array like) dicts (not nested). I have a hunch, that nested dicts might get things much more complicated and/or inefficient.

Another idea that I'm having is writing some C functions that help me to store the dict data directly in C instead of storing it first in Tcl, then transfer to C. For example, I would need a Tcl/C function that does the equivalent to "dict set", let's say "c2tcl::dict_set". Then I could access the value with "c2tcl::dict_get". When I need to perform large operations on the whole dict, then I don't need to transfer it from Tcl to C first, because it's already in C. Not sure though how this copes with Tcl treads.

I hope you can give me some advice to any of the two methos, before I start putting the effort in programing.

Many thanks
Alexandru

* Alexandru <alexandru.dadalau@meshparts.de>
| I have some C functions that perform fast operations on lists of numbers.
| Until now, I transfer Tcl data in the shape of lists to those C functions.
| In some cases the Tcl data is stored in dictionaries so I run some Tcl
| loops over the Tcl dict, put the needed data into lists and finally
| pass the lists to the C function.
| Since performance is paramount, I'm thinking that the above method might not be the fastest.
| If I would directly pass the Tcl dict to the C function, would that be faster?

Not copying data sounds always faster to me...

https://www.tcl.tk/man/tcl8.6/TclLib/DictObj.html

lists the C interface to dicts. Basically you get the TclObjs for the
keys and/or values in the dict. You would then call Tcl_GetIntFromObj()
on the value ptr.

| What if the Tcl dict is "nested" so there are multiple keys that lead to a value?

You would need some information on the nesting depth, since the value
has no "I'm a dict" label attached. You could check whether
Tcl_GetIntFromObj(valueptr) is successful and if not, try to use it as
multiple-level dict.

| Can I (efficiently) access nested dicts with the C API?

I would say 'yes', since in nested dicts the values are themselves just
dicts instead of plain... well... 'values'. Haven't tried that myself, though.

HTH
R'

Am 16.01.2024 um 16:17 schrieb Ralf Fassel:
> | Can I (efficiently) access nested dicts with the C API?
>
> I would say 'yes', since in nested dicts the values are themselves just
> dicts instead of plain... well... 'values'. Haven't tried that myself, though.

I confirm that this works: nested dicts from C.
There is no buildin for it, so it should be programmed manually:

TCL_OBJ * subdict;

if (TCL_OK == Tcl_DictObjGet(interp, dictPtr, keyPtr, subdict)
&& TCL_OK == Tcl_DictObjGet(interp, subdict, keyPtr, valuePtrPtr) )

Harald Oehlmann schrieb am Dienstag, 16. Januar 2024 um 16:43:55 UTC+1:
> Am 16.01.2024 um 16:17 schrieb Ralf Fassel:
> > | Can I (efficiently) access nested dicts with the C API?
> >
> > I would say 'yes', since in nested dicts the values are themselves just
> > dicts instead of plain... well... 'values'. Haven't tried that myself, though.
> I confirm that this works: nested dicts from C.
> There is no buildin for it, so it should be programmed manually:
>
> TCL_OBJ * subdict;
>
> if (TCL_OK == Tcl_DictObjGet(interp, dictPtr, keyPtr, subdict)
> && TCL_OK == Tcl_DictObjGet(interp, subdict, keyPtr, valuePtrPtr) )

Thanks Harald and Ralf for the hints.
I'll try to implement it and measure the speed.

Regards
Alexandru

* Harald Oehlmann <wortkarg3@yahoo.com>
| Am 16.01.2024 um 16:17 schrieb Ralf Fassel:
| > | Can I (efficiently) access nested dicts with the C API?
| > I would say 'yes', since in nested dicts the values are themselves
| > just
| > dicts instead of plain... well... 'values'. Haven't tried that myself, though.
>
| I confirm that this works: nested dicts from C.
| There is no buildin for it, so it should be programmed manually:
>
| TCL_OBJ * subdict;
>
| if (TCL_OK == Tcl_DictObjGet(interp, dictPtr, keyPtr, subdict)

I *think* that needs to be

Tcl_DictObjGet(interp, dictPtr, keyPtr, &subdict)

since Tcl_DictObjGet() takes a TclObj** as last parameter.

R'