GDPR: Anonymize WordPress user IP address in comments, supports IP4 and IP6

anonymize-comment-ip.php

<?php

if ( true == apply_filters( 'is_gdpr', true ) ) {
	add_filter( 'pre_comment_user_ip', function( $ip ) {
		$packed_in_addr  = inet_pton( $ip );
        	if ( 4 == strlen( $packed_in_addr ) ) {
			return inet_ntop( inet_pton( $ip ) & inet_pton( '255.255.0.0' ) );
		} else {
			return inet_ntop( inet_pton( $ip ) & inet_pton( 'ffff:ffff:ffff:ffff:0000:0000:0000:0000' ) );
		}
	} );
}

ip4-anonymize-comment-ip.php

<?php
add_filter( 'pre_comment_user_ip', function( $ip ) {
	return inet_ntop( inet_pton( $ip ) & inet_pton( '255.255.0.0' ) ); // return an IP address in the form of nnn.nnn.0.0
} );

wp-anonymize-comment-ip.php

<?php
// using the new wp_privacy_anonymize_ip function, available in WordPress 4.9.6
if ( function_exists( 'wp_privacy_anonymize_ip' ) ) {
	add_filter( 'pre_comment_user_ip', function( $ip ) {
		return wp_privacy_anonymize_ip( $ip );
	}
}