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#include <stdint.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
#ifndef PAGE_SIZE
#define PAGE_SIZE 4096
#endif
struct Page {
uint8_t *elements;
Page *next;
Page *prev;
uint16_t gap_start;
uint16_t gap_end;
uint16_t element_count;
Page() {
elements = new uint8_t[PAGE_SIZE];
gap_start = 0;
gap_end = PAGE_SIZE;
element_count = 0;
next = nullptr;
prev = nullptr;
}
~Page() {
if (prev) prev->next = next;
if (next) next->prev = prev;
delete[] elements;
}
void split() {
Page *front = new Page();
memcpy(front->elements, elements + PAGE_SIZE / 2, PAGE_SIZE / 2);
front->gap_start = PAGE_SIZE / 2;
front->gap_end = PAGE_SIZE;
front->element_count = PAGE_SIZE / 2;
gap_start = PAGE_SIZE / 2;
gap_end = PAGE_SIZE;
element_count = PAGE_SIZE / 2;
if (next) {
next->prev = front;
}
front->next = next;
front->prev = this;
next = front;
}
void copy_to(Page *dest) {
memcpy(dest->elements, elements, PAGE_SIZE);
dest->gap_start = gap_start;
dest->gap_end = gap_end;
dest->element_count = element_count;
}
void operator++(int) {
assert(gap_end < PAGE_SIZE);
elements[gap_start] = elements[gap_end];
gap_start++;
gap_end++;
}
void operator--(int) {
assert(gap_start > 0);
gap_end--;
gap_start--;
elements[gap_end] = elements[gap_start];
}
void push(uint8_t c) {
assert(element_count < PAGE_SIZE);
elements[gap_start] = c;
gap_start++;
element_count++;
}
void pop() {
assert(gap_start > 0);
gap_start--;
element_count--;
}
};
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