function configuration_hash_field in Configuration Management 7
File
- includes/configuration.field.inc, line 245 
Code
function configuration_hash_field($identifier) {
  // Export just the field we're tracking.
  module_load_include('inc', 'configuration', 'configuration.export');
  $data = field_configuration_export_options();
  // Export the field we just saved and evaluate the export to hash
  $code = field_configuration_export_render('configuration', array(
    $data[$identifier],
  ));
  eval(array_pop($code));
  return md5(serialize($fields[$identifier]));
}