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/* fib, but the cache is a directory of files
* cache/
* 0 -> 0
* 1 -> 1
* 2 -> 1
* 3 -> 2
* ...
* unix filesystem required
*/
#include <dirent.h>
#include <string.h>
#include <stdio.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
static const char CACHE_DIR[] = "cache";
static const int BUF_SIZE = 30;
static const int PATH_SIZE = 30;
static const int N_STR_SIZE = 30;
static const int LOF_INITIAL_SIZE = 1;
long read_from_cache(char* path) {
char buf[BUF_SIZE];
int fd = open(path, O_RDONLY);
if (fd == -1) {
close(fd);
return 0;
}
if (!read(fd, buf, BUF_SIZE)) {
close(fd);
return 0;
}
close(fd);
return strtol(buf, NULL, 10);
}
long write_to_cache(char* path, long result) {
char buf[BUF_SIZE];
int fd = open(path, O_CREAT | O_RDWR, S_IRUSR | S_IWUSR);
sprintf(buf, "%ld", result);
if (fd == -1) {
close(fd);
return 0;
}
if (!write(fd, buf, strlen(buf))) {
close(fd);
return 0;
}
close(fd);
return 1;
}
long init_cache() {
char path_to_0[PATH_SIZE];
char path_to_1[PATH_SIZE];
sprintf(path_to_0, "%s/%s", CACHE_DIR, "0");
sprintf(path_to_1, "%s/%s", CACHE_DIR, "1");
if (!write_to_cache(path_to_0, 0)) {
return 0;
}
if (!write_to_cache(path_to_1, 1)) {
return 0;
}
return 1;
}
long get_list_of_files(long** list_of_files, long curr_size) {
mkdir("cache", 0777);
struct dirent *d;
DIR* cache_dir = opendir(CACHE_DIR);
if (!cache_dir) {
closedir(cache_dir);
return 0;
}
init_cache();
while ((d = readdir(cache_dir)) != NULL) {
if (d->d_type == DT_REG) {
*((*list_of_files) + curr_size - 1) = strtol(d->d_name, NULL, 10);
curr_size++;
*list_of_files = realloc(*list_of_files, curr_size * sizeof(long));
}
}
closedir(cache_dir);
return curr_size - 1;
}
int is_in_cache(long* list_of_files, long size_of_lof, long n) {
for (int i = 0; i < size_of_lof; i++) {
if (list_of_files[i] == n) return 1;
}
return 0;
}
long fib(long n) {
char n_str[N_STR_SIZE];
char path[PATH_SIZE];
long* list_of_files = malloc(sizeof(long));
long size_of_lof = get_list_of_files(&list_of_files, LOF_INITIAL_SIZE);
sprintf(n_str, "%ld", n);
sprintf(path, "%s/%s", CACHE_DIR, n_str);
if (is_in_cache(list_of_files, size_of_lof, n)) {
free(list_of_files);
long cached_value = read_from_cache(path);
return cached_value;
}
free(list_of_files);
long toCache = fib(n-1) + fib(n-2);
write_to_cache(path, toCache);
return toCache;
}
int main() {
printf("FIB RESULT: %ld\n", fib(13));
}
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