<?php 
/** 
 * Copyright 2016 Facebook, Inc. 
 * 
 * You are hereby granted a non-exclusive, worldwide, royalty-free license to 
 * use, copy, modify, and distribute this software in source code or binary 
 * form for use in connection with the web services and APIs provided by 
 * Facebook. 
 * 
 * As with any software that integrates with the Facebook platform, your use 
 * of this software is subject to the Facebook Developer Principles and 
 * Policies [http://developers.facebook.com/policy/]. This copyright notice 
 * shall be included in all copies or substantial portions of the software. 
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL 
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING 
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER 
 * DEALINGS IN THE SOFTWARE. 
 * 
 */ 
 
/** 
 * @see https://github.com/sarciszewski/php-future/blob/master/src/Security.php#L37-L51 
 */ 
if (!function_exists('hash_equals')) { 
    function hash_equals($knownString, $userString) 
    { 
        if (function_exists('mb_strlen')) { 
            $kLen = mb_strlen($knownString, '8bit'); 
            $uLen = mb_strlen($userString, '8bit'); 
        } else { 
            $kLen = strlen($knownString); 
            $uLen = strlen($userString); 
        } 
        if ($kLen !== $uLen) { 
            return false; 
        } 
        $result = 0; 
        for ($i = 0; $i < $kLen; $i++) { 
            $result |= (ord($knownString[$i]) ^ ord($userString[$i])); 
        } 
 
        // They are only identical strings if $result is exactly 0... 
        return 0 === $result; 
    } 
} 
 
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