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// SPDX-License-Identifier: LGPL-2.1+
/*
* Copyright (C) 2017 Red Hat, Inc.
*/
#include "c-list-util.h"
/*****************************************************************************/
/**
* c_list_relink:
* @lst: the head list entry
*
* Takes an invalid list, that has undefined prev pointers.
* Only the next pointers are valid, and the tail's next
* pointer points to %NULL instead of the head.
*
* c_list_relink() fixes the list by updating all prev pointers
* and close the circular linking by pointing the tails' next
* pointer to @lst.
*
* The use of this function is to do a bulk update, that lets the
* list degredate by not updating the prev pointers. At the end,
* the list can be fixed by c_list_relink().
*/
void
c_list_relink(CList *lst)
{
CList *ls, *ls_prev;
ls_prev = lst;
ls = lst->next;
do {
ls->prev = ls_prev;
ls_prev = ls;
ls = ls->next;
} while (ls);
ls_prev->next = lst;
lst->prev = ls_prev;
}
/*****************************************************************************/
static CList *
_c_list_srt_split(CList *ls)
{
CList *ls2;
ls2 = ls;
ls = ls->next;
if (!ls)
return NULL;
do {
ls = ls->next;
if (!ls)
break;
ls = ls->next;
ls2 = ls2->next;
} while (ls);
ls = ls2->next;
ls2->next = NULL;
return ls;
}
static CList *
_c_list_srt_merge(CList *ls1, CList *ls2, CListSortCmp cmp, const void *user_data)
{
CList *ls;
CList head;
ls = &head;
for (;;) {
/* while invoking the @cmp function, the list
* elements are not properly linked. Don't try to access
* their next/prev pointers. */
if (cmp(ls1, ls2, user_data) <= 0) {
ls->next = ls1;
ls = ls1;
ls1 = ls1->next;
if (!ls1)
break;
} else {
ls->next = ls2;
ls = ls2;
ls2 = ls2->next;
if (!ls2)
break;
}
}
ls->next = ls1 ?: ls2;
return head.next;
}
typedef struct {
CList *ls1;
CList *ls2;
char ls1_sorted;
} SortStack;
static CList *
_c_list_sort(CList *ls, CListSortCmp cmp, const void *user_data)
{
/* reserve a huge stack-size. We need roughly log2(n) entries, hence this
* is much more we will ever need. We don't guard for stack-overflow either. */
SortStack stack_arr[70];
SortStack *stack_head = stack_arr;
stack_arr[0].ls1 = ls;
/* A simple top-down, non-recursive, stable merge-sort.
*
* Maybe natural merge-sort would be better, to do better for
* partially sorted lists. */
_split:
stack_head[0].ls2 = _c_list_srt_split(stack_head[0].ls1);
if (stack_head[0].ls2) {
stack_head[0].ls1_sorted = 0;
stack_head[1].ls1 = stack_head[0].ls1;
stack_head++;
goto _split;
}
_backtrack:
if (stack_head == stack_arr)
return stack_arr[0].ls1;
stack_head--;
if (!stack_head[0].ls1_sorted) {
stack_head[0].ls1 = stack_head[1].ls1;
stack_head[0].ls1_sorted = 1;
stack_head[1].ls1 = stack_head[0].ls2;
stack_head++;
goto _split;
}
stack_head[0].ls1 = _c_list_srt_merge(stack_head[0].ls1, stack_head[1].ls1, cmp, user_data);
goto _backtrack;
}
/**
* c_list_sort_headless:
* @lst: the list.
* @cmp: compare function for sorting. While comparing two
* CList elements, their next/prev pointers are in undefined
* state.
* @user_data: user data for @cmp.
*
* Sorts the list @lst according to @cmp. Contrary to
* c_list_sort(), @lst is not the list head but a
* valid entry as well. This function returns the new
* list head.
*/
CList *
c_list_sort_headless(CList *lst, CListSortCmp cmp, const void *user_data)
{
if (!c_list_is_empty(lst)) {
lst->prev->next = NULL;
lst = _c_list_sort(lst, cmp, user_data);
c_list_relink(lst);
}
return lst;
}
/**
* c_list_sort:
* @head: the list head.
* @cmp: compare function for sorting. While comparing two
* CList elements, their next/prev pointers are in undefined
* state.
* @user_data: user data for @cmp.
*
* Sorts the list @head according to @cmp.
*/
void
c_list_sort(CList *head, CListSortCmp cmp, const void *user_data)
{
if (!c_list_is_empty(head) && head->next->next != head) {
head->prev->next = NULL;
head->next = _c_list_sort(head->next, cmp, user_data);
c_list_relink(head);
}
}
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