On 24/07/17 08:00PM, Chandra Pratap wrote:
> On Wed, 17 Jul 2024 at 18:09, Karthik Nayak <karthik.188@xxxxxxxxx> wrote:
> >
> > Chandra Pratap <chandrapratap3519@xxxxxxxxx> writes:
> >
> > > +struct curry {
> > > + void *last;
> > > +};
> > > +
> > > +static void check_increasing(void *arg, void *key)
> > > +{
> > > + struct curry *c = arg;
> > > + if (c->last)
> > > + check_int(t_compare(c->last, key), <, 0);
> > > + c->last = key;
> > > +}
> > > +
> > > +static void t_tree(void)
> > > +{
> > > + struct tree_node *root = NULL;
> > > + void *values[11] = { 0 };
> >
> > Although we were comparing 'char' above, here we have a 'void *' array.
> > Why?
>
> The array is passed as a parameter to the 'tree_search()' function which
> requires a void * parameter (i.e. a generic pointer). In the comparison
> function (also passed as a parameter), we cast it to our expected type
> (a character pointer) and then perform the required comparison.
The point of `values` is to provide a set of values of type `void **` to
be inserted in the tree. As far as I can tell, there is no reason for
`values` to be initialized to begin with and is a bit misleading. Might
be reasonable to remove its initialization here.
> > > + struct tree_node *nodes[11] = { 0 };
> > > + size_t i = 1;
> > > + struct curry c = { 0 };
> > > +
> > > + do {
> > > + nodes[i] = tree_search(values + i, &root, &t_compare, 1);
> > > + i = (i * 7) % 11;
> >
> > It gets weirder, we calculate 'i' as {7, 5, 2, 3, 10, 4, 6, 9, 8, 1}. We
> > use that to index 'values', but values is '0' initialized, so we always
> > send '0' to tree_search? Doesn't that make this whole thing a moot? Or
> > did I miss something?
>
> We don't use 'i' to index 'values[]', we use it to calculate the next pointer
> address to be passed to the 'tree_search()' function (the pointer that is 'i'
> ahead of the pointer 'values'), which isn't 0.
The `i = (i * 7) % 11;` is used to deterministically generate numbers
1-10 in a psuedo-random fashion. These numbers are used as memory
offsets to be inserted into the tree. I suspect the psuedo-randomness is
useful keys should be ordered when inserted into the tree and that is
later validated as part of the in-order traversal that is performed.
While rather compact, I find the test setup here to rather difficult to
parse. It might be a good idea to either provide comments explaining
this test setup or consider refactoring it. Honestly, I'd personally
perfer the tree setup be done more explicitly as I think it would make
understanding the test much easier.
-Justin
