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<?php function foo1($string, $with) { if (!$bytes = static::byteLength($with)) { return true; } // Warning check, see http://php.net/manual/en/function.substr-compare.php#refsect1-function.substr-compare-returnvalues if (static::byteLength($string) < $bytes) { return false; } return substr_compare($string, $with, -$bytes); } function foo2($string, $with) { if (!$bytes = static::byteLength($with)) { return true; } // Warning check, see http://php.net/manual/en/function.substr-compare.php#refsect1-function.substr-compare-returnvalues if (static::byteLength($string) < $bytes) { return false; } return substr_compare($string, $with, -$bytes, $bytes); } var_dump(foo1('a', 'a')); var_dump(foo2('a', 'a')); var_dump(foo1('', '')); var_dump(foo2('', '')); var_dump(foo1('a', '')); var_dump(foo2('a', '')); var_dump(foo1('', 'a')); var_dump(foo2('', 'a'));