Detect whether an Apple ][ .dsk .do or .po disk image file is in DOS 3 or ProDOS format and in DOS 3 or ProDOS sector order

apple2dskdetect.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>

#define TRACKS 35
#define SECTORS_PER_TRACK 16
#define SECTOR_SIZE 256

int main(int argc, char *argv[]) {
    if (argc != 2) {
        fprintf(stderr, "Usage: %s <path_to_disk_image>\n", argv[0]);
        return EXIT_FAILURE;
    }

    FILE *file = fopen(argv[1], "rb");
    if (file) {
        struct stat st;
        if (fstat(fileno(file), &st) == 0) {
            if (st.st_size == (TRACKS * SECTORS_PER_TRACK * SECTOR_SIZE)) {
                unsigned char t0s4[SECTOR_SIZE];
                unsigned char t0s11[SECTOR_SIZE];
                unsigned char t17s0[SECTOR_SIZE + 3];

                fseek(file, (0 * SECTORS_PER_TRACK + 4) * SECTOR_SIZE, SEEK_SET);
                fread(t0s4, sizeof(unsigned char), SECTOR_SIZE, file);

                fseek(file, (0 * SECTORS_PER_TRACK + 11) * SECTOR_SIZE, SEEK_SET);
                fread(t0s11, sizeof(unsigned char), SECTOR_SIZE, file);

                fseek(file, (17 * SECTORS_PER_TRACK) * SECTOR_SIZE, SEEK_SET);
                fread(t17s0, sizeof(unsigned char), SECTOR_SIZE + 3, file);

                unsigned char *pro[2] = {t0s4, t0s11};

                for (int i = 0; i < 2; i++) {
                    if ((pro[i][4] >> 4) == 0xf &&
                            (pro[i][4] & 0x0f) > 0 && (pro[i][4] & 0x0f) <= 15 &&
                            pro[i][5] >= 'A' && pro[i][5] <= 'Z') {
                        printf("Looks like ProDOS in %s order: '%s'\n", i == 0 ? "ProDOS" : "DOS 3", argv[1]);
                    }
                }

                unsigned char *dos = t17s0;
                if (dos[0x27] == 122 && dos[0x30] < TRACKS && (dos[0x31] == 1 || dos[0x31] == 0xff) &&
                    dos[0x34] == 35 && dos[0x35] == 16 && dos[0x36] == 0 && dos[0x37] == 1) {
                    if (dos[SECTOR_SIZE + 1] == 0 && dos[SECTOR_SIZE + 2] == 0) {
                        printf("Looks like DOS 3.3 in DOS 3 order: '%s'\n", argv[1]);
                    } else if (dos[SECTOR_SIZE + 1] == 17 && dos[SECTOR_SIZE + 2] == 13) {
                        printf("Looks like DOS 3.3 in ProDOS order: '%s'\n", argv[1]);
                    }
                }
            }
        }
        fclose(file);
    }

    return EXIT_SUCCESS;
}