cbtree.h

/*
 * crit-bit tree implementation, does no allocations internally
 * For more information on crit-bit trees: https://cr.yp.to/critbit.html
 * Based on Adam Langley's adaptation of Dan Bernstein's public domain code
 * git clone https://github.com/agl/critbit.git
 *
 * This is adapted to store arbitrary data (not just NUL-terminated C strings
 * and allocates no memory internally.  The user needs to allocate
 * "struct cb_node" and provide `key_offset` to indicate where the key can be
 * found relative to the `struct cb_node` for memcmp.
 * If "klen" is variable, then it should be embedded into the key.
 * Recursion is bound by the maximum value of "klen" used.
 */
#ifndef CBTREE_H
#define CBTREE_H

struct cb_node;
struct cb_node {
	struct cb_node *child[2];
	/*
	 * n.b. uint32_t for `byte' is excessive for OIDs,
	 * we may consider shorter variants if nothing else gets stored.
	 */
	uint32_t byte;
	uint8_t otherbits;
};

struct cb_tree {
	struct cb_node *root;
	ptrdiff_t key_offset;
};

static inline void cb_init(struct cb_tree *t,
			   ptrdiff_t key_offset)
{
	struct cb_tree blank = {
		.key_offset = key_offset,
	};
	memcpy(t, &blank, sizeof(*t));
}

struct cb_node *cb_lookup(struct cb_tree *, const uint8_t *k, size_t klen);
struct cb_node *cb_insert(struct cb_tree *, struct cb_node *, size_t klen);

/*
 * Callback invoked by `cb_each()` for each node in the critbit tree. A return
 * value of 0 will cause the iteration to continue, a non-zero return code will
 * cause iteration to abort. The error code will be relayed back from
 * `cb_each()` in that case.
 */
typedef int (*cb_iter)(struct cb_node *, void *arg);

int cb_each(struct cb_tree *, const uint8_t *kpfx, size_t klen,
	    cb_iter, void *arg);

#endif /* CBTREE_H */