<?php

/*
 * This file is part of the eluceo/iCal package.
 *
 * (c) Markus Poerschke <markus@eluceo.de>
 *
 * This source file is subject to the MIT license that is bundled
 * with this source code in the file LICENSE.
 */

namespace Eluceo\iCal\Util;

class ComponentUtil
{
    /**
     * Folds a single line.
     *
     * According to RFC 5545, all lines longer than 75 characters should be folded
     *
     * @see https://tools.ietf.org/html/rfc5545#section-5
     * @see https://tools.ietf.org/html/rfc5545#section-3.1
     *
     * @param $string
     *
     * @return array
     */
    public static function fold($string)
    {
        $lines = [];
        while (strlen($string) > 0) {
            if (strlen($string) > 75) {
                $lines[] = mb_strcut($string, 0, 75, 'utf-8') . "\r\n";
                $str = ' ' . mb_strcut($string, 75, strlen($string), 'utf-8');
            } else {
                $lines[] = $string;
                $str = '';
                break;
            }
        }
        return $lines;
    }
}

<?php

/*
 * This file is part of the eluceo/iCal package.
 *
 * (c) Markus Poerschke <markus@eluceo.de>
 *
 * This source file is subject to the MIT license that is bundled
 * with this source code in the file LICENSE.
 */

namespace Eluceo\iCal\Util;

class ComponentUtil
{
    /**
     * Folds a single line.
     *
     * According to RFC 5545, all lines longer than 75 characters should be folded
     *
     * @see https://tools.ietf.org/html/rfc5545#section-5
     * @see https://tools.ietf.org/html/rfc5545#section-3.1
     *
     * @param $string
     *
     * @return array
     */
    public static function fold($string)
    {
        $lines = [];
        $array = preg_split('/(?<!^)(?!$)/u', $string);

        $line = '';
        $lineNo = 0;
        foreach ($array as $char) {
            $charLen = strlen($char);
            $lineLen = strlen($line);
            if ($lineLen + $charLen > 75) {
                $line = ' ' . $char;
                ++$lineNo;
            } else {
                $line .= $char;
            }
            $lines[$lineNo] = $line;
        }

        return $lines;
    }
}

--- 
+++ 
@@ -28,22 +28,16 @@
     public static function fold($string)
     {
         $lines = [];
-        $array = preg_split('/(?<!^)(?!$)/u', $string);
-
-        $line = '';
-        $lineNo = 0;
-        foreach ($array as $char) {
-            $charLen = strlen($char);
-            $lineLen = strlen($line);
-            if ($lineLen + $charLen > 75) {
-                $line = ' ' . $char;
-                ++$lineNo;
+        while (strlen($string) > 0) {
+            if (strlen($string) > 75) {
+                $lines[] = mb_strcut($string, 0, 75, 'utf-8') . "\r\n";
+                $str = ' ' . mb_strcut($string, 75, strlen($string), 'utf-8');
             } else {
-                $line .= $char;
+                $lines[] = $string;
+                $str = '';
+                break;
             }
-            $lines[$lineNo] = $line;
         }
-
         return $lines;
     }
 }
Optimize Performance for long lines (use mb_strcut() instead of pred_split())
