Task 31 (sort file.bin inplace).c

#include <stdlib.h>
#include <err.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/types.h>
#include <stdint.h>
#include <errno.h>
#include <unistd.h>

int main(int argc, char **argv){
	if(argc != 2){
		errx(1, "Invalid number of arguments. Usage: %s <file.bin>", argv[0]);
	}

	char *file = argv[1];

	struct stat st;

	if(stat(file, &st) == -1){
		err(2, "could not stat file %s", file);
	}

	if(!(st.st_mode & S_IRUSR) || !(st.st_mode & S_IWUSR)){
		errx(3, "file %s not readable or not writable", file);
	}

	/*
	if(st.st_size > UINT64_MAX){
		warnx("small chance of overfloating");
	}
	*/

	uint64_t counting[256] = { 0 };
	uint16_t level[256];
	for (uint16_t j = 0; j< 256; ++j){
		level[j] = 1;
	}

	ssize_t fd = open(file, O_RDWR);
	if(fd == -1){
		err(4, "error while opening file %s", file);
	}

	ssize_t read_sz;
	uint8_t b;	
	
	while((read_sz = read(fd, &b, sizeof(b))) == sizeof(b)){ 
		++counting[b];
		if(counting[b] == UINT64_MAX){
			counting[b] = 0;
			++level[b];
		}
	}	
	if(read_sz == -1){
		const int olderrno = errno;
		close(fd);
		errno = olderrno;
		err(5, "error while reading file %s", file);
	}

	if(lseek(fd, 0, SEEK_SET) == -1){
		const int olderrno = errno;
		close(fd);
		errno = olderrno;
		err(6, "error while lseek file %s", file);
	}

	uint16_t i = 0;

	for(; i < 256; ++i){
		while(level[i]--){
			b = i;
			while(counting[i]--){
				if(write(fd, &b, sizeof(b)) != sizeof(b)){
					const int olderrno = errno;
					close(fd);
					errno = olderrno;
					err(7, "error while writing into file %s", file);
				}
			}
			counting[i] = UINT64_MAX;
		}
	}

	close(fd);
	exit(0);
}