Parser::parse_iprp( int $num_remaining_bytes )

  private function parse_iprp( $num_remaining_bytes ) {
    do {
      $box    = new Box();
      $status = $box->parse( $this->handle, $this->num_parsed_boxes, $num_remaining_bytes );
      if ( $status != FOUND ) {
        return $status;
      }

      if ( $box->type == 'ipco' ) {
        $status = $this->parse_ipco( $box->content_size );
        if ( $status != NOT_FOUND ) {
          return $status;
        }
      } else if ( $box->type == 'ipma' ) {
        // See ISO/IEC 23008-12:2017(E) 9.3.2
        $num_read_bytes = 4;
        if ( $box->content_size < $num_read_bytes ) {
          return INVALID;
        }
        if ( !( $data = read( $this->handle, $num_read_bytes ) ) ) {
          return TRUNCATED;
        }
        $entry_count        = read_big_endian( $data, 4 );
        $id_num_bytes       = ( $box->version < 1 ) ? 2 : 4;
        $index_num_bytes    = ( $box->flags & 1 ) ? 2 : 1;
        $essential_bit_mask = ( $box->flags & 1 ) ? 0x8000 : 0x80;

        for ( $entry = 0; $entry < $entry_count; ++$entry ) {
          if ( $entry >= MAX_PROPS ||
               count( $this->features->props ) >= MAX_PROPS ) {
            $this->data_was_skipped = true;
            break;
          }
          $num_read_bytes += $id_num_bytes + 1;
          if ( $box->content_size < $num_read_bytes ) {
            return INVALID;
          }
          if ( !( $data = read( $this->handle, $id_num_bytes + 1 ) ) ) {
            return TRUNCATED;
          }
          $item_id           = read_big_endian(
              substr( $data, 0, $id_num_bytes ), $id_num_bytes );
          $association_count = read_big_endian(
              substr( $data, $id_num_bytes, 1 ), 1 );

          for ( $property = 0; $property < $association_count; ++$property ) {
            if ( $property >= MAX_PROPS ||
                 count( $this->features->props ) >= MAX_PROPS ) {
              $this->data_was_skipped = true;
              break;
            }
            $num_read_bytes += $index_num_bytes;
            if ( $box->content_size < $num_read_bytes ) {
              return INVALID;
            }
            if ( !( $data = read( $this->handle, $index_num_bytes ) ) ) {
              return TRUNCATED;
            }
            $value          = read_big_endian( $data, $index_num_bytes );
            // $essential = ($value & $essential_bit_mask);  // Unused.
            $property_index = ( $value & ~$essential_bit_mask );
            if ( $property_index <= MAX_VALUE && $item_id <= MAX_VALUE ) {
              $prop_count = count( $this->features->props );
              $this->features->props[$prop_count]                 = new Prop();
              $this->features->props[$prop_count]->property_index = $property_index;
              $this->features->props[$prop_count]->item_id        = $item_id;
            } else {
              $this->data_was_skipped = true;
            }
          }
          if ( $property < $association_count ) {
            break; // Do not read garbage.
          }
        }

        // If all features are available now, do not look further.
        $status = $this->features->get_primary_item_features();
        if ( $status != NOT_FOUND ) {
          return $status;
        }

        // Mostly if 'data_was_skipped'.
        if ( !skip( $this->handle, $box->content_size - $num_read_bytes ) ) {
          return TRUNCATED;
        }
      } else {
        if ( !skip( $this->handle, $box->content_size ) ) {
          return TRUNCATED;
        }
      }
      $num_remaining_bytes -= $box->size;
    } while ( $num_remaining_bytes > 0 );
    return NOT_FOUND;
  }