src/tools/fixup_amiga_boot_checksum/fixup_amiga_boot_checksum.c

   1 #include <stdio.h>
   2 #include <stdint.h>
   3 #include <fcntl.h>
   4 #include <unistd.h>
   5 #include <netinet/in.h>
   6
   7 #define BB_SIZE (2*512)
   8
   9 int main(int argc, char **argv)
  10 {
  11         int fd;
  12         unsigned int i;
  13         uint32_t sum;
  14         uint8_t bootblock[BB_SIZE];
  15         uint32_t *p = (uint32_t *)bootblock;
  16         fd = open(argv[1], O_RDWR);
  17         if (fd < 0) {
  18                 return 1;
  19         }
  20         if (read(fd, bootblock, BB_SIZE) < BB_SIZE) {
  21                 perror("read");
  22                 return 1;
  23         }
  24         if (ntohl(p[0]) != 'DOS\0') {
  25                 fprintf(stderr, "bad bootblock signature!\n");
  26                 return 1;
  27         }
  28         p[1] = 0;
  29         for (sum = 0, i = 0; i < (BB_SIZE)/sizeof(uint32_t); i++) {
  30                 uint32_t old = sum;
  31                 // big endian
  32                 sum += ntohl(*p++);
  33                 // overflow
  34                 if (sum < old)
  35                         sum++;
  36         }
  37         sum = ~sum;
  38         //fprintf(stderr, "checksum: 0x%lx\n", (long)sum);
  39         // big endian
  40         ((uint32_t *)bootblock)[1] = htonl(sum);
  41         lseek(fd, 0LL, SEEK_SET);
  42         write(fd, bootblock, BB_SIZE);
  43         return 0;
  44 }