/* 
 * http://eab.abime.net/showpost.php?p=895070&postcount=6 
 * Makes a disk image of 901120 (0xdc000) bytes.
 * Calculates boot block checksum.
 */

#include <stdio.h>
#include <string.h>
#include <stdint.h>

#define DISKSIZE (0xdc000)

uint8_t image[DISKSIZE];


static void boot_chksum(uint8_t *p)
{
  uint32_t oldchk,chk=0;
  int i;

  memset(p+4,0,4);
  for (i=0; i<1024; i+=4) {
    oldchk = chk;
    chk += ((uint32_t)p[i+0] << 24) | ((uint32_t)p[i+1] << 16) |
      ((uint32_t)p[i+2] << 8) | p[i+3];
    if (chk < oldchk)
      ++chk;  /* carry */
  }

  chk = ~chk;
  p[4] = (uint8_t)((chk >> 24) & 0xff);
  p[5] = (uint8_t)((chk >> 16) & 0xff);
  p[6] = (uint8_t)((chk >> 8) & 0xff);
  p[7] = (uint8_t)(chk & 0xff);
}


int main(int argc,char *argv[])
{
  FILE *f;
  int rc = 1;
  size_t len;

  if (argc == 2) {
    if ((f = fopen(argv[1],"rb"))) {
      len = fread(image,1,DISKSIZE,f);
      if (len > 0) {
        if (len < DISKSIZE)
          memset(image+len,0,DISKSIZE-len);
        boot_chksum(image);
        fwrite(image,1,DISKSIZE,stdout);
        rc = 0;
      }
      else
        fprintf(stderr,"Image read error!\n");
    }
    else
      fprintf(stderr,"Cannot open '%s'!\n",argv[0]);  
  }
  else
    fprintf(stderr,"Usage: %s <image data>\n",argv[0]);

  return rc;
}