Chandra Pratap <chandrapratap3519@xxxxxxxxx> writes:
> On Thu, 18 Jul 2024 at 03:45, Justin Tobler <jltobler@xxxxxxxxx> wrote:
>>
>> 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.
>
> The thing is, the values[] array being 0-initialized makes debugging
> a lot easier in the case of a test failure, so I'm not very sure about
> getting rid of the 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.
>
> That's right, the randomness of the insertion order is helpful in validating
> that the tree-functions 'tree_search()' and 'infix_walk()' work according
> to their defined behaviour.
>
>> 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.
>
> This probably ties in with the comments by Patrick on the previous iteration
> of this patch, that using 'tree_search()' to insert tree nodes leads to
> confusion. Solving that would require efforts outside the scope of this
> patch series though, so I'm more inclined towards providing comments
> and other ways of simplifying this subroutine.
Agreed that refactoring `tree_search()` probably is out of scope here.
But rewriting the test is definitely something we can do.
Perhaps:
static void t_tree(void)
{
struct tree_node *root = NULL;
int values[11] = {7, 5, 2, 3, 10, 4, 6, 9, 8, 1};
struct tree_node *nodes[11] = { 0 };
size_t i = 1;
struct curry c = { 0 };
// Insert values to the tree by passing '1' as the last argument.
for (i = 1; i < ARRAY_SIZE(values); i++) {
nodes[i] = tree_search(&values[i], &root, &t_compare, 1);
}
for (i = 1; i < ARRAY_SIZE(nodes); i++) {
check_pointer_eq(values[i], nodes[i]->key);
check_pointer_eq(nodes[i], tree_search(values + i, &root, &t_compare, 0));
}
infix_walk(root, check_increasing, &c);
tree_free(root);
}
Wouldn't this have the same effect while making it much easier to read?
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