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/* SPDX-License-Identifier: GPL-3.0-or-later */
/* Copyright 2021 - 2022, Kim Kuparinen < kimi.h.kuparinen@gmail.com > */
/**
* @file sp_tree.c
* Implementation of my sp_trees. An sp_tree is a mix of rb-trees and avl-trees,
* with slightly faster insertion but worse tree depth on average.
*
* See https://github.com/Kimplul/sptree
*
* \todo Document sp_tree algorithm better.
*/
#include <apos/sp_tree.h>
/**
* Basic BST left turn.
* Drop node \c n down to the left side of the right node, letting it take
* the place of \c n.
*
* @param n Node to turn left.
*/
static void __sp_turn_left(struct sp_node *n)
{
struct sp_node *l = sp_left(n);
struct sp_node *p = sp_paren(n);
sp_paren(l) = sp_paren(n);
sp_left(n) = sp_right(l);
sp_paren(n) = l;
sp_right(l) = n;
if (p && sp_left(p) == n)
sp_left(p) = l;
else if (p)
sp_right(p) = l;
if (sp_left(n))
sp_lparen(n) = n;
}
/**
* Basic BST right turn.
* Drop node \c n down to the right side of the left node, letting it take the
* place of \c n.
*
* Does not check if right node exists.
*
* @param n Node to turn right.
*/
static void __sp_turn_right(struct sp_node *n)
{
struct sp_node *r = sp_right(n);
struct sp_node *p = sp_paren(n);
sp_paren(r) = sp_paren(n);
sp_right(n) = sp_left(r);
sp_paren(n) = r;
sp_left(r) = n;
if (p && sp_left(p) == n)
sp_left(p) = r;
else if (p)
sp_right(p) = r;
if (sp_right(n))
sp_rparen(n) = n;
}
/**
* Calculate approximate balance of node, based on height hints.
*
* @param n Node to calculate balance for.
* @return Balance of node.
*/
static int_fast16_t __sp_balance(struct sp_node *n)
{
int_fast16_t l = 0;
int_fast16_t r = 0;
if (sp_left(n))
l = sp_left(n)->hint + 1;
if (sp_right(n))
r = sp_right(n)->hint + 1;
return l - r;
}
/**
* Get highest hint.
*
* @param n Node to calculate highest hint for.
* @return Highest hint.
*/
static int_fast16_t __sp_max_hint(struct sp_node *n)
{
int_fast16_t l = 0;
int_fast16_t r = 0;
if (sp_left(n))
l = sp_left(n)->hint + 1;
if (sp_right(n))
r = sp_right(n)->hint + 1;
if (l > r)
return l;
else
return r;
}
/**
* Balance tree, moving up from c n.
*
* @param root Root of tree.
* @param n Node to start balancing operation from.
*/
static void __sp_update(struct sp_node **root, struct sp_node *n)
{
while (n) {
int b = __sp_balance(n);
int prev_hint = n->hint;
struct sp_node *p = sp_paren(n);
if (b < -1) {
/* leaning to the right */
if (n == *root)
*root = sp_right(n);
__sp_turn_right(n);
}
else if (b > 1) {
/* leaning to the left */
if (n == *root)
*root = sp_left(n);
__sp_turn_left(n);
}
n->hint = __sp_max_hint(n);
if (n->hint == 0 || n->hint != prev_hint)
n = p;
else
return;
}
}
void sp_insert(struct sp_node **root, struct sp_node *p, struct sp_node *n,
enum sp_dir d)
{
if (!*root) {
*root = n;
return;
}
if (d == LEFT)
sp_left(p) = n;
else
sp_right(p) = n;
sp_paren(n) = p;
__sp_update(root, n);
}
/**
* Replace node \c n with \c l, pulling of the righthand side of \n.
*
* @param n Node to replace.
* @param r Node to replace with.
*/
static void __sp_replace_right(struct sp_node *n, struct sp_node *r)
{
struct sp_node *p = sp_paren(n);
struct sp_node *rp = sp_paren(r);
if (sp_left(rp) == r) {
sp_left(rp) = sp_right(r);
if (sp_right(r))
sp_rparen(r) = rp;
}
if (sp_paren(rp) == n)
sp_paren(rp) = r;
sp_paren(r) = p;
sp_left(r) = sp_left(n);
if (sp_right(n) != r) {
sp_right(r) = sp_right(n);
sp_rparen(n) = r;
}
if (p && sp_left(p) == n)
sp_left(p) = r;
else if (p)
sp_right(p) = r;
if (sp_left(n))
sp_lparen(n) = r;
}
/**
* Replace node \c n with node \c l, pulling up the lefthand side of \c n.
*
* @param n Node to replace.
* @param l Node to replace with.
*/
static void __sp_replace_left(struct sp_node *n, struct sp_node *l)
{
struct sp_node *p = sp_paren(n);
struct sp_node *lp = sp_paren(l);
if (sp_right(lp) == l) {
sp_right(lp) = sp_left(l);
if (sp_left(l))
sp_lparen(l) = lp;
}
if (sp_paren(lp) == n)
sp_paren(lp) = l;
sp_paren(l) = p;
sp_right(l) = sp_right(n);
if (sp_left(n) != l) {
sp_left(l) = sp_left(n);
sp_lparen(n) = l;
}
if (p && sp_left(p) == n)
sp_left(p) = l;
else if (p)
sp_right(p) = l;
if (sp_right(n))
sp_rparen(n) = l;
}
void sp_remove(struct sp_node **root, struct sp_node *del)
{
if (sp_right(del)) {
struct sp_node *least = sp_first(sp_right(del));
if (del == *root)
*root = least;
__sp_replace_right(del, least);
__sp_update(root, sp_right(least));
return;
}
if (sp_left(del)) {
struct sp_node *most = sp_last(sp_left(del));
if (del == *root)
*root = most;
__sp_replace_left(del, most);
__sp_update(root, sp_left(most));
return;
}
if (del == *root) {
*root = 0;
return;
}
/* empty node */
struct sp_node *paren = sp_paren(del);
if (sp_left(paren) == del)
sp_left(paren) = 0;
else
sp_right(paren) = 0;
__sp_update(root, paren);
}
struct sp_node *sp_first(struct sp_node *n)
{
if (!sp_left(n))
return n;
return sp_first(sp_left(n));
}
struct sp_node *sp_last(struct sp_node *n)
{
if (!sp_right(n))
return n;
return sp_last(sp_right(n));
}
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