Make if statement using pointers explicitly check whether the value is
NULL or not.
The C standard does not say that the null pointer is the same as the
pointer to memory address 0 and because of this is a good practice
always compare with the macro NULL.
Signed-off-by: Flavio Ceolin <flavio.ceolin@intel.com>
The scheduler priq implementation was taking advantage of a subtle
behavior of the way the tree presents the order of its arguments (the
node being inserted is always first). But it turns out the tree got
that wrong in one spot.
As this was subtle voodoo to begin with, it should have been
documented first. Similarly add a little code to the test case to
guarantee this in the future.
Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
Works mostly like the list enumeration macros. Implemented by fairly
clever alloca trickery and some subtle "next node" logic. More
convenient for many uses, can be early-exited, but has somewhat larger
code size than rb_walk().
Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
Returns true if the specified node is in the tree. Allows the tree to
be used for "set" style semantics along with a lessthan_fn that simply
compares the nodes by their address.
Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
A balanced tree implementation for Zephyr as we grow into bigger
regimes where simpler data structures aren't appropriate.
This implements an intrusive balanced tree that guarantees O(log2(N))
runtime for all operations and amortized O(1) behavior for creation
and destruction of whole trees. The algorithms and naming are
conventional per existing academic and didactic implementations, c.f.:
https://en.wikipedia.org/wiki/Red%E2%80%93black_tree
The implementation is size-optimized to prioritize runtime memory
usage. The data structure is intrusive, which is to say the struct
rbnode handle is intended to be placed in a separate struct the same
way other such structures (e.g. Zephyr's dlist list) and requires no
data pointer to be stored in the node. The color bit is unioned with
a pointer (fairly common for such libraries). Most notably, there is
no "parent" pointer stored in the node, the upper structure of the
tree being generated dynamically via a stack as the tree is recursed.
So the overall memory overhead of a node is just two pointers,
identical with a doubly-linked list.
Code size above dlist is about 2-2.5k on most architectures, which is
significant by Zephyr standards but probably still worthwhile in many
situations.
Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
Flavio Ceolin