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/* single header b-tree implementation by Abdellah El Morabit */
#ifndef B_TREE_H
#define B_TREE_H
// maximum height of the tree the lower the lower the lower amount
// of disk reads which translates into faster?
#define B_TREE_ORDER 4
typedef struct b_tree_node b_tree_node;
struct b_tree_node
{
// store the values
string8 keys[B_TREE_ORDER - 1];
// TODO(nasr): replace with something more generic?
// NOTE(nasr): cons of void * -> no type safety
// is there a way to still have some sort of that?
void *payload_per_key[B_TREE_ORDER - 1];
b_tree_node *parent;
// handle to store children faster than linked list
// because now we can iterate over the nodes instead of having cache misses
// when jumping through linked nodes
b_tree_node *children[B_TREE_ORDER];
// this shouldn't change things but could be a performance improvement on a bigger scale??
s32 *max_children;
// NOTE(nasr): reference count ::: check how many leaves are using this node
// also not needed for now because we don't free individual node because of arena allocator
// s32 *refc;
s32 key_count;
b32 leaf;
};
typedef struct b_tree b_tree;
struct b_tree
{
// NOTE(nasr): make sure this always stays in memory
// so that initial fetch never requires a disk read
b_tree_node *root;
};
#ifdef B_TREE_IMPLEMENTATION
///////////////////////////////////////////////////////////////////////////////
//- b_tree.c
// TODO(nasr): 1. splitting the tree when getting too big? (horizontally) 2. joining trees?
internal b_tree_node *
btree_node_alloc(mem_arena *arena)
{
b_tree_node *node = PushStructZero(arena, b_tree_node);
node->leaf = 1;
return node;
}
// NOTE(nasr): @return the index of the found element
internal s32
btree_node_find_pos(string8 value, b_tree_node *node)
{
s32 i = 0;
for (; i < node->key_count && string8_cmp(node->keys[i], value) < 0; ++i);
return i;
}
internal void
b_tree_create(mem_arena *arena, b_tree *tree)
{
tree->root = btree_node_alloc(arena);
tree->root->leaf = 1;
tree->root->key_count = 0;
}
// NOTE(nasr): nodes that get passed as parameters should've already been loaded into memory
internal void *
b_tree_search(b_tree_node *node, string8 key)
{
s32 i = btree_node_find_pos(key, node);
if (i < node->key_count && string8_cmp(node->keys[i], key) == 0)
{
return node->payload_per_key[i];
}
if (node->leaf)
{
return NULL;
}
return b_tree_search(node->children[i], key);
}
// TODO(nasr): split node when key_count == B_TREE_ORDER - 1 (node is full)
internal void
b_tree_insert(mem_arena *arena, b_tree *tree, string8 key, void *payload)
{
b_tree_node *current_node = tree->root;
if (current_node->leaf)
{
// find the insertion position and shift keys right to make room
s32 i = btree_node_find_pos(key, current_node);
for (s32 j = current_node->key_count; j > i; --j)
{
current_node->keys[j] = current_node->keys[j - 1];
current_node->payload_per_key[j] = current_node->payload_per_key[j - 1];
}
current_node->keys[i] = key;
current_node->payload_per_key[i] = payload;
if(current_node->key_count < (B_TREE_ORDER - 1))
{
current_node->key_count += 1;
}
else {
// TODO(nasr): creating a new branch / tree?
}
}
// TODO(nasr): internal node case walk down then split on the way back up
}
internal void
b_tree_write(b_tree *bt)
{
// TODO(nasr): write the b_tree to disk
}
#endif /* B_TREE_IMPLEMENTATION */
#endif /* B_TREE_H */
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