Sorting atom callback lists

void Atom::add_callback(int flag)

{

  int ifix;

  int ifix, i, j;

  // find the fix

  // if find NULL ptr:

  for (ifix = 0; ifix < modify->nfix; ifix++)

    if (modify->fix[ifix] == NULL) break;

  // add callback to lists, reallocating if necessary

  // insert callback into sorted lists, reallocating if necessary

  // sorting is required in cases where fixes were replaced as it ensures atom

  // data is read/written/transfered in the same order that fixes are called

  if (flag == 0) {

    if (nextra_grow == nextra_grow_max) {

      nextra_grow_max += DELTA;

      memory->grow(extra_grow,nextra_grow_max,"atom:extra_grow");

    }

    for(i = 0; i < nextra_grow; i ++)

        if(ifix < extra_grow[i]) break;

    if(i == nextra_grow) {

      extra_grow[nextra_grow] = ifix;

    } else {

      for(j = nextra_grow-1; j >= i; j --)

          extra_grow[j+1] = extra_grow[j];

      extra_grow[i] = ifix;

    }

    nextra_grow++;

  } else if (flag == 1) {

    if (nextra_restart == nextra_restart_max) {

      nextra_restart_max += DELTA;

      memory->grow(extra_restart,nextra_restart_max,"atom:extra_restart");

    }

    for(i = 0; i < nextra_restart; i ++)

        if(ifix < extra_restart[i]) break;

    if(i == nextra_restart) {

      extra_restart[nextra_restart] = ifix;

    } else {

      for(j = nextra_restart-1; j >= i; j --)

          extra_restart[j+1] = extra_restart[j];

      extra_restart[i] = ifix;

    }     

    nextra_restart++;

  } else if (flag == 2) {

    if (nextra_border == nextra_border_max) {

      nextra_border_max += DELTA;

      memory->grow(extra_border,nextra_border_max,"atom:extra_border");

    }

    for(i = 0; i < nextra_border; i ++)

        if(ifix < extra_border[i]) break;

    if(i == nextra_border) {

      extra_border[nextra_border] = ifix;

    } else {

      for(j = nextra_border-1; j >= i; j --)

          extra_border[j+1] = extra_border[j];

      extra_border[i] = ifix;

    }

    nextra_border++;

  }

}