tomato-testing/toxcore/list.c

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/* SPDX-License-Identifier: GPL-3.0-or-later
* Copyright © 2016-2018 The TokTok team.
* Copyright © 2014 Tox project.
*/
/**
* Simple struct with functions to create a list which associates ids with data
* - Allows for finding ids associated with data such as IPs or public keys in a short time
* - Should only be used if there are relatively few add/remove calls to the list
*/
#include "list.h"
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include "ccompat.h"
/**
* Basically, the elements in the list are placed in order so that they can be searched for easily
* - each element is seen as a big-endian integer when ordering them
* - the ids array is maintained so that each id always matches
* - the search algorithm cuts down the time to find the id associated with a piece of data
* at the cost of slow add/remove functions for large lists
* - Starts at `1/2` of the array, compares the element in the array with the data,
* then moves `+/- 1/4` of the array depending on whether the value is greater or lower,
* then `+- 1/8`, etc, until the value is matched or its position where it should be in the array is found
* - some considerations since the array size is never perfect
*/
static int32_t
list_index(uint32_t i)
{
return ~i;
}
/** @brief Find data in list
*
* @retval >=0 index of data in array
* @retval <0 no match, returns index (return value is `list_index(index)`) where
* the data should be inserted
*/
non_null()
static int find(const BS_List *list, const uint8_t *data)
{
// should work well, but could be improved
if (list->n == 0) {
return list_index(0);
}
uint32_t i = list->n / 2; // current position in the array
uint32_t delta = i / 2; // how much we move in the array
if (delta == 0) {
delta = 1;
}
int d = -1; // used to determine if closest match is found
// closest match is found if we move back to where we have already been
while (true) {
const int r = memcmp(data, list->data + list->element_size * i, list->element_size);
if (r == 0) {
return i;
}
if (r > 0) {
// data is greater
// move down
i += delta;
if (d == 0 || i == list->n) {
// reached bottom of list, or closest match
return list_index(i);
}
delta = delta / 2;
if (delta == 0) {
delta = 1;
d = 1;
}
} else {
// data is smaller
if (d == 1 || i == 0) {
// reached top or list or closest match
return list_index(i);
}
// move up
i -= delta;
delta = delta / 2;
if (delta == 0) {
delta = 1;
d = 0;
}
}
}
}
/**
* Resizes the list.
*
* @return true on success.
*/
non_null()
static bool resize(BS_List *list, uint32_t new_size)
{
if (new_size == 0) {
bs_list_free(list);
return true;
}
uint8_t *data = (uint8_t *)realloc(list->data, list->element_size * new_size);
if (data == nullptr) {
return false;
}
list->data = data;
int *ids = (int *)realloc(list->ids, sizeof(int) * new_size);
if (ids == nullptr) {
return false;
}
list->ids = ids;
return true;
}
int bs_list_init(BS_List *list, uint32_t element_size, uint32_t initial_capacity)
{
// set initial values
list->n = 0;
list->element_size = element_size;
list->capacity = 0;
list->data = nullptr;
list->ids = nullptr;
if (initial_capacity != 0) {
if (!resize(list, initial_capacity)) {
return 0;
}
}
list->capacity = initial_capacity;
return 1;
}
void bs_list_free(BS_List *list)
{
if (list == nullptr) {
return;
}
// free both arrays
free(list->data);
list->data = nullptr;
free(list->ids);
list->ids = nullptr;
}
int bs_list_find(const BS_List *list, const uint8_t *data)
{
const int r = find(list, data);
// return only -1 and positive values
if (r < 0) {
return -1;
}
return list->ids[r];
}
bool bs_list_add(BS_List *list, const uint8_t *data, int id)
{
// find where the new element should be inserted
// see: return value of find()
int i = find(list, data);
if (i >= 0) {
// already in list
return false;
}
i = ~i;
// increase the size of the arrays if needed
if (list->n == list->capacity) {
// 1.5 * n + 1
const uint32_t new_capacity = list->n + list->n / 2 + 1;
if (!resize(list, new_capacity)) {
return false;
}
list->capacity = new_capacity;
}
// insert data to element array
memmove(list->data + (i + 1) * list->element_size, list->data + i * list->element_size,
(list->n - i) * list->element_size);
memcpy(list->data + i * list->element_size, data, list->element_size);
// insert id to id array
memmove(&list->ids[i + 1], &list->ids[i], (list->n - i) * sizeof(int));
list->ids[i] = id;
// increase n
++list->n;
return true;
}
bool bs_list_remove(BS_List *list, const uint8_t *data, int id)
{
const int i = find(list, data);
if (i < 0) {
return false;
}
if (list->ids[i] != id) {
// this should never happen
return false;
}
// decrease the size of the arrays if needed
if (list->n < list->capacity / 2) {
const uint32_t new_capacity = list->capacity / 2;
if (resize(list, new_capacity)) {
list->capacity = new_capacity;
}
}
--list->n;
memmove(list->data + i * list->element_size, list->data + (i + 1) * list->element_size,
(list->n - i) * list->element_size);
memmove(&list->ids[i], &list->ids[i + 1], (list->n - i) * sizeof(int));
return true;
}