@since 3.0.0:
	 *
	 * @see is_valid_url()
	 * @see get_size_from_file_name()
	 * @see get_url_without_dimensions()
	 * @see set_additional_srcset()
	 * @see generate_srcset()
	 * @see maybe_generate_srcset()
	 * @see is_supported_path()
	 */

	/**
	 * Check if we can use the image URL in CDN.
	 *
	 * @param string $url Image URL.
	 *
	 * @return bool
	 * @since 3.0
	 *
	 */
	private function is_valid_url( $url ) {
		$parsed_url = wp_parse_url( $url );

		if ( ! $parsed_url ) {
			return false;
		}

		// No host or path found.
		if ( ! isset( $parsed_url['host'] ) || ! isset( $parsed_url['path'] ) ) {
			return false;
		}

		// If not supported extension - return false.
		if ( ! in_array( strtolower( pathinfo( $parsed_url['path'], PATHINFO_EXTENSION ) ), $this->supported_extensions, true ) ) {
			return false;
		}

		return true;
	}

	/**
	 * Try to determine height and width from strings WP appends to resized image filenames.
	 *
	 * @param string $src The image URL.
	 *
	 * @return array An array consisting of width and height.
	 * @since 3.0
	 *
	 */
	private function get_size_from_file_name( $src ) {
		$size = array();

		if ( preg_match( '/-(\d+)x(\d+)\.(?:' . implode( '|', $this->supported_extensions ) . ')$/i', $src, $size ) ) {
			// Get size and width.
			$width  = (int) $size[1];
			$height = (int) $size[2];

			// Handle retina images.
			if ( strpos( $src, '@2x' ) ) {
				$width  = 2 * $width;
				$height = 2 * $height;
			}

			// Return width and height as array.
			if ( $width && $height ) {
				return array( $width, $height );
			}
		}

		return array( false, false );
	}

	/**
	 * Filters an array of image srcset values, and add additional values.
	 *
	 * @param array $sources An array of image urls and widths.
	 * @param array $size_array Array of width and height values in pixels.
	 * @param string $url Image URL.
	 * @param array $image_meta The image metadata.
	 * @param string $image_src The src of the image.
	 *
	 * @return array $sources
	 * @since 3.0
	 *
	 */
	private function set_additional_srcset( $sources, $size_array, $url, $image_meta, $image_src = '' ) {
		$content_width = $this->settings->max_content_width();

		// If url is empty, try to get from src.
		if ( empty( $url ) ) {
			$url = $this->urls_utils->get_url_without_dimensions( $image_src );
		}

		// We need to add additional dimensions.
		$full_width     = $image_meta['width'];
		$full_height    = $image_meta['height'];
		$current_width  = $size_array[0];
		$current_height = $size_array[1];
		// Get width and height calculated by WP.
		list( $constrained_width, $constrained_height ) = wp_constrain_dimensions( $full_width, $full_height, $current_width, $current_height );

		// Calculate base width.
		// If $constrained_width sizes are smaller than current size, set maximum content width.
		if ( abs( $constrained_width - $current_width ) <= 1 && abs( $constrained_height - $current_height ) <= 1 ) {
			$base_width = $content_width;
		} else {
			$base_width = $current_width;
		}

		$current_widths = array_keys( $sources );
		$new_sources    = array();

		/**
		 * Filter to add/update/bypass additional srcsets.
		 *
		 * If empty value or false is retured, additional srcset
		 * will not be generated.
		 *
		 * @param array|bool $additional_multipliers Additional multipliers.
		 */
		$additional_multipliers = apply_filters(
			'smush_srcset_additional_multipliers',
			array(
				0.2,
				0.4,
				0.6,
				0.8,
				1,
				1.5,
				2,
				3,
			)
		);

		// Continue only if additional multipliers found or not skipped.
		// Filter already documented in class-cdn.php.
		if ( $this->cdn_helper->skip_image_url( $url, false ) || empty( $additional_multipliers ) ) {
			return $sources;
		}

		// Loop through each multipliers and generate image.
		foreach ( $additional_multipliers as $multiplier ) {
			// New width by multiplying with original size.
			$new_width = (int) ( $base_width * $multiplier );

			// In most cases - going over the current width is not recommended and probably not what the user is expecting.
			if ( $new_width > $current_width ) {
				continue;
			}

			// If a nearly sized image already exist, skip.
			foreach ( $current_widths as $_width ) {
				// If +- 50 pixel difference - skip.
				if ( abs( $_width - $new_width ) < 50 || ( $new_width > $full_width ) ) {
					continue 2;
				}
			}

			// We need the width as well...
			$dimensions = wp_constrain_dimensions( $current_width, $current_height, $new_width );

			// Arguments for cdn url.
			$args = array(
				'size' => "{$new_width}x{$dimensions[1]}",
			);

			// Add new srcset item.
			$new_sources[ $new_width ] = array(
				'url'        => $this->cdn_helper->generate_cdn_url( $url, $args ),
				'descriptor' => 'w',
				'value'      => $new_width,
			);
		}

		// Assign new srcset items to existing ones.
		if ( ! empty( $new_sources ) ) {
			// Loop through each items and replace/add.
			foreach ( $new_sources as $_width_key => $_width_values ) {
				$sources[ $_width_key ] = $_width_values;
			}
		}

		return $sources;
	}

	/**
	 * Try to generate the srcset for the image.
	 *
	 * @param string $src Image source.
	 *
	 * @return array|bool
	 * @since 3.0
	 *
	 */
	public function generate_srcset( $src, $attachment_id = 0, $width = 0, $height = 0 ) {
		$priority = $this->get_cdn_srcset_priority();
		add_filter( 'wp_calculate_image_srcset', array( $this, 'update_image_srcset' ), $priority, 5 );
		list( $srcset, $sizes ) = $this->srcset_helper->generate_srcset_and_sizes(
			$src,
			$attachment_id,
			$width,
			$height
		);
		remove_filter( 'wp_calculate_image_srcset', array( $this, 'update_image_srcset' ), $priority );

		return array( $srcset, $sizes );
	}

	/**
	 * @return int
	 */
	private function get_cdn_srcset_priority(): int {
		return defined( 'WP_SMUSH_CDN_DELAY_SRCSET' ) && WP_SMUSH_CDN_DELAY_SRCSET ? 1000 : 99;
	}

}
<br />
<b>Fatal error</b>:  Uncaught Error: Class &quot;Smush\Core\CDN\CDN_Srcset_Controller&quot; not found in /home/cpaherna/public_html/wp-content/plugins/wp-smushit/core/modules/class-cdn.php:32
Stack trace:
#0 /home/cpaherna/public_html/wp-content/plugins/wp-smushit/core/class-modules.php(151): Smush\Core\Modules\CDN-&gt;__construct()
#1 /home/cpaherna/public_html/wp-content/plugins/wp-smushit/core/class-core.php(158): Smush\Core\Modules-&gt;__construct()
#2 /home/cpaherna/public_html/wp-content/plugins/wp-smushit/core/class-stats.php(104): Smush\Core\Core-&gt;init()
#3 /home/cpaherna/public_html/wp-content/plugins/wp-smushit/wp-smush.php(387): Smush\Core\Stats-&gt;__construct()
#4 /home/cpaherna/public_html/wp-content/plugins/wp-smushit/wp-smush.php(307): WP_Smush-&gt;init()
#5 /home/cpaherna/public_html/wp-content/plugins/wp-smushit/wp-smush.php(258): WP_Smush-&gt;__construct()
#6 /home/cpaherna/public_html/wp-includes/class-wp-hook.php(324): WP_Smush::get_instance('')
#7 /home/cpaherna/public_html/wp-includes/class-wp-hook.php(348): WP_Hook-&gt;apply_filters(NULL, Array)
#8 /home/cpaherna/public_html/wp-includes/plugin.php(517): WP_Hook-&gt;do_action(Array)
#9 /home/cpaherna/public_html/wp-settings.php(555): do_action('plugins_loaded')
#10 /home/cpaherna/public_html/wp-config.php(96): require_once('/home/cpaherna/...')
#11 /home/cpaherna/public_html/wp-load.php(50): require_once('/home/cpaherna/...')
#12 /home/cpaherna/public_html/wp-blog-header.php(13): require_once('/home/cpaherna/...')
#13 /home/cpaherna/public_html/index.php(17): require('/home/cpaherna/...')
#14 {main}
  thrown in <b>/home/cpaherna/public_html/wp-content/plugins/wp-smushit/core/modules/class-cdn.php</b> on line <b>32</b><br />