Adds file size to a file field

theme_file_link.php

//ADDS FILESIZE TO A FILE FIELD
function the_aim_theme_file_link($variables) {
  $file = $variables['file'];
  $icon_directory = $variables['icon_directory'];

  $url = file_create_url($file->uri);
  $icon = theme('file_icon', array('file' => $file, 'icon_directory' => $icon_directory));

  // Set options as per anchor format described at
  // http://microformats.org/wiki/file-format-examples
  $options = array(
    'attributes' => array(
      'type' => $file->filemime . '; length=' . $file->filesize,
    ),
  );

  // Use the description as the link text if available.
  if (empty($file->description)) {
    $link_text = $file->filename;
  }
  else {
    $link_text = $file->description;
    $options['attributes']['title'] = check_plain($file->filename);
  }

  return '<span class="file">' . $icon . ' ' . l($link_text, $url, $options) . ' (' . __format_file_fize_size($file->filesize) . ')</span>';
}

//CUSTOM FUNCTION TO FORMAT FILESIZE FROM BYTES TO READABLE
function __format_file_fize_size( $size, $display_bytes=false ) {
  if( $size < 1024 )
    $filesize = $size . ' bytes';
  elseif( $size >= 1024 && $size < 1048576 )
    $filesize = round( $size/1024, 2 ) . ' KB';

  elseif( $size >= 1048576 )
    $filesize = round( $size/1048576, 2 ) . ' MB';

  if( $size >= 1024 && $display_bytes )
    $filesize = $filesize . ' (' . $size . ' bytes)';

  return $filesize;
}