/*
 * Extract uclinux kernel image from Billion/Telewell firmware update
 *
 * Written by Harry Sintonen <sintonen@iki.fi>.
 * Public Domain.
 *
 * USAGE
 *
 * ./twuclinixextract < bla.afw > bla.img
 *
 * NOTES
 *
 * Doesn't decode the image in any way. If someone has ideas
 * how to do that, please let me know.
 *
 * Works with at least:
 * http://www.telewell.fi/paivitykset/tw_ea501/Telewell-TWEA501v3A-V1.23-B002a.zip
 * http://www.telewell.fi/paivitykset/tw_ea501/Telewell-TWEA501v2A-V1.23-B002a.zip
 * http://www.telewell.fi/paivitykset/tw_ea510/Telewell-TWEA510v2A-V1.23-B002a.zip
 * http://www.telewell.fi/paivitykset/tw_ea510/Telewell-TWEA510v2rA-V1.23-B002a.zip
 * http://www.telewell.fi/paivitykset/tw_ea510/Telewell-TWEA510v3A-V1.23-B002a.zip
 */

#include <stdio.h>
#include <stdlib.h>

#ifdef __GNUC__
void peof(void) __attribute__ ((__noreturn__));
#endif

void peof(void)
{
  fprintf(stderr, "premature EOF\n");
  exit(20);
}

void myseek(FILE *fh, int cnt)
{
  while (cnt--)
  {
    if (fgetc(fh) == EOF)
    {
      peof();
    }
  }
}

unsigned int be32(FILE *fh)
{
  unsigned int v = 0;
  int i;

  for (i = 0; i < 4; i++)
  {
    int c;

    if ((c = fgetc(fh)) == EOF)
    {
      peof();
    }
    v = (v << 8) | (unsigned char) c;
  }
  return v;
}

int main(void)
{
  unsigned int size;

  myseek(stdin, 0x3c);
  size = be32(stdin);

  fprintf(stderr, "size: %u\n", size);
  if (size < 0x40)
  {
    fprintf(stderr, "bogus size\n");
    return 20;
  }

  size -= 0x40;
  myseek(stdin, 0x100 - 0x40);

  while (size--)
  {
    int c;

    c = getchar();
    if (c == EOF ||
        putchar(c) == EOF)
    {
      peof();
    }
  }
  fprintf(stderr, "Ok\n");

  return 0;
}