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#include <stdint.h>
#include <string.h>
#include <stdlib.h>
#define PAGE_SIZE 4096
struct page {
uint8_t *buffer;
uint16_t gap_start;
uint16_t gap_end;
uint16_t element_count;
struct page *next;
struct page *prev;
};
struct point {
struct page *current_page;
uint16_t index;
};
uint16_t index_to_offset(struct page *page, uint16_t index) {
if (index < page->gap_start) {
return index;
} else {
return index + (page->gap_end - page->gap_start);
}
}
void move_point_forward(struct point *point) {
struct page *page = point->current_page;
if (point->index < page->element_count) {
point->index++;
}
if (point->index == page->element_count && page->next) {
point->index = 0;
point->current_page = page->next;
}
}
void move_point_backward(struct point *point) {
struct page *page = point->current_page;
if (point->index == 0 && page->prev) {
point->index = page->prev->element_count;
point->current_page = page->prev;
}
if (point->index > 0) {
point->index--;
}
}
struct page *new_page() {
struct page *result = malloc(sizeof(struct page));
result->buffer = malloc(PAGE_SIZE);
result->gap_start = 0;
result->gap_end = PAGE_SIZE;
result->next = 0;
result->prev = 0;
return result;
}
void split_page(struct page *back) {
struct page *front = new_page();
memcpy(front->buffer, back->buffer + PAGE_SIZE / 2, PAGE_SIZE / 2);
front->gap_start = PAGE_SIZE / 2;
front->gap_end = PAGE_SIZE;
front->element_count = PAGE_SIZE / 2;
back->gap_start = PAGE_SIZE / 2;
back->gap_end = PAGE_SIZE;
back->element_count = PAGE_SIZE / 2;
if (back->next) {
back->next->prev = front;
}
front->next = back->next;
front->prev = back;
back->next = front;
}
void free_page(struct page *page) {
if (page->prev) {
page->prev->next = page->next;
}
if (page->next) {
page->next->prev = page->prev;
}
free(page);
}
void move_gap_forward(struct page *page) {
page->buffer[page->gap_start] = page->buffer[page->gap_end];
page->gap_start++;
page->gap_end++;
}
void move_gap_backward(struct page *page) {
page->gap_end--;
page->gap_start--;
page->buffer[page->gap_end] = page->buffer[page->gap_start];
}
void move_gap(struct page *page, uint16_t index) {
while (page->gap_end < index_to_offset(page, index)) {
move_gap_forward(page);
}
while (page->gap_end > index_to_offset(page, index)) {
move_gap_backward(page);
}
}
void insert_at_point(struct point *point, uint8_t c) {
struct page *page = point->current_page;
if (page->gap_start == page->gap_end) {
split_page(page);
if (point->index >= PAGE_SIZE / 2) {
page = page->next;
point->current_page = page;
point->index -= PAGE_SIZE / 2;
}
}
move_gap(page, point->index);
page->buffer[page->gap_start] = c;
page->gap_start++;
page->element_count++;
move_point_forward(point);
}
void delete_at_point(struct point *point) {
struct page *page = point->current_page;
if (page->element_count == 0) {
if (page->prev) {
page = page->prev;
free_page(point->current_page);
point->current_page = page;
point->index = page->element_count;
} else if (page->next) {
page = page->next;
free_page(point->current_page);
point->current_page = page;
point->index = 0;
}
}
move_gap(page, point->index);
if (page->gap_start != 0) {
page->gap_start--;
page->element_count--;
move_point_backward(point);
}
}
uint8_t get_element(struct point *point) {
return point->current_page->buffer[index_to_offset(point->current_page, point->index)];
}
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