te')); return $arr; } /* 遍历用户所有主题 * @param $uid 用户ID * @param int $page 页数 * @param int $pagesize 每页记录条数 * @param bool $desc 排序方式 TRUE降序 FALSE升序 * @param string $key 返回的数组用那一列的值作为 key * @param array $col 查询哪些列 */ function thread_tid_find_by_uid($uid, $page = 1, $pagesize = 1000, $desc = TRUE, $key = 'tid', $col = array()) { if (empty($uid)) return array(); $orderby = TRUE == $desc ? -1 : 1; $arr = thread_tid__find($cond = array('uid' => $uid), array('tid' => $orderby), $page, $pagesize, $key, $col); return $arr; } // 遍历栏目下tid 支持数组 $fid = array(1,2,3) function thread_tid_find_by_fid($fid, $page = 1, $pagesize = 1000, $desc = TRUE) { if (empty($fid)) return array(); $orderby = TRUE == $desc ? -1 : 1; $arr = thread_tid__find($cond = array('fid' => $fid), array('tid' => $orderby), $page, $pagesize, 'tid', array('tid', 'verify_date')); return $arr; } function thread_tid_delete($tid) { if (empty($tid)) return FALSE; $r = thread_tid__delete(array('tid' => $tid)); return $r; } function thread_tid_count() { $n = thread_tid__count(); return $n; } // 统计用户主题数 大数量下严谨使用非主键统计 function thread_uid_count($uid) { $n = thread_tid__count(array('uid' => $uid)); return $n; } // 统计栏目主题数 大数量下严谨使用非主键统计 function thread_fid_count($fid) { $n = thread_tid__count(array('fid' => $fid)); return $n; } ?>javascript - Bitwise operations on non numbers - Stack Overflow

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    Somehow, JavaScript makes sense of the bitwise operations NaN ^ 1, Infinity ^ 1 and even 'a' ^ 1 (all evaluate to 1).

    What are the rules governing bitwise operators on non numbers? Why do all the examples above evaluate to 1?

    Somehow, JavaScript makes sense of the bitwise operations NaN ^ 1, Infinity ^ 1 and even 'a' ^ 1 (all evaluate to 1).

    What are the rules governing bitwise operators on non numbers? Why do all the examples above evaluate to 1?

    • javascript
    • operators
    • bit-manipulation
    Share Improve this question edited Jun 14, 2012 at 17:00 Paul 142k28 gold badges282 silver badges270 bronze badges asked Jun 14, 2012 at 16:52 RandomblueRandomblue 116k150 gold badges362 silver badges557 bronze badges 0
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    2 Answers 2

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    According to the ES5 spec, when doing bitwise operations, all operands are converted to ToInt32 (which first calls ToNumber. If the value is NaN or Infinity, it's converted to 0).

    Thus: NaN ^ 1 => 0 XOR 1 => 1

    ECMA-262 defines in 11.10 that arguments of binary bitwise operators are converted with ToInt32. And 9.5 that explains ToInt32 says in its first two points:

    1. Let number be the result of calling ToNumber on the input argument.
    2. If number is NaN, +0, -0, +Inf, or -Inf, return +0.

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