datsum

datsum.c

/*
 * datsum.c
 * Generates checksum for Taiko no Tatsujin iOS dat file
 *
 * NOTE: For 32-bit build, set _FILE_OFFSET_BITS=64
 */
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>

#define INIT_F1 0x72ce14c2
#define INIT_F2 0xfc3e151f

uint32_t cksum(FILE *fdat) {
    uint32_t checksum, f1, f2, f3, i, shifts;
    size_t datsize;
    off_t offset;
    uint8_t buf[1024] = {0}, ctr = 0;

    fseeko(fdat, 0, SEEK_END);
    datsize = ftello(fdat);
    fseeko(fdat, 0, SEEK_SET);

    f1 = ((uint32_t)(datsize & 0xffffffff)) ^ INIT_F1;
    f2 = INIT_F2;

    for (offset = 0; offset < datsize; offset += 1024) {
        fread(buf, 1, 1024, fdat);
        for (i = 0; i < 1024; i++) {
            if ((i & 0xf) == 7) {
                f3 = f1 + (buf[i] << 6);
            } else {
                shifts = ((ctr & 0xf) + 5);
                f3 = f1 - (buf[i] << shifts);
            }
            f1 = f3 ^ f2;
            f2 ^= INIT_F1;
        }
        ctr += 1;
    }
 
    checksum = f1 & 0x7fffffff;
    checksum |= (f1 >> 3);
    return checksum;
}

int main(int argc, char *argv[]) {
    int exit_code = 0, file_index;
    struct stat sb;

    if (argc >= 2) {
        for (file_index = 1; file_index < argc; file_index++) {
            if (lstat(argv[file_index], &sb) == -1) {
                perror("lstat()");
                exit_code = 1;
            } else if (!S_ISREG(sb.st_mode)) {
                printf("%s: Is not a regular file\n", argv[file_index]);
                exit_code = 1;
            } else {
                FILE *fdat = fopen(argv[file_index], "rb");
                if (fdat == NULL) {
                    perror("fopen()");
                    exit_code = 1;
                } else {
                    printf("%u  %s\n", cksum(fdat), argv[file_index]);
                    fclose(fdat);
                }
            }
        }
    } else {
        printf("Usage: %s <datfile> ...\n", argv[0]);
        exit_code = 1;
    }
    return exit_code;
}