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; } ?>How to convert one byte (8 bit) to signed integer in JavaScript? - Stack Overflow

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    How to convert one byte (8 bit) to signed integer in JavaScript? - Stack Overflow

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    I need to convert one byte into java script signed integer. I have checked this link which converts 2 bytes , but how could I downgrade and convert only one byte?

    for example 0x0A would be 10, how about 0xD4?

    I need to convert one byte into java script signed integer. I have checked this link which converts 2 bytes , but how could I downgrade and convert only one byte?

    for example 0x0A would be 10, how about 0xD4?

    • javascript
    • byte
    • bit
    Share Improve this question asked Jun 13, 2019 at 9:58 Ehsan Zargar ErshadiEhsan Zargar Ershadi 24.8k18 gold badges67 silver badges95 bronze badges 2
    • parseInt("0xD4", 16) // from 16 bit , parseInt("473", 8) // from 8 bit , parseInt("110011", 2) // from 2 bit , – Arshpreet Wadehra Commented Jun 13, 2019 at 10:01
    • 1 Please read the question carefully, your solution is working only for unsigned values, for some reason I know that 0xD4 should be a negative value – Ehsan Zargar Ershadi Commented Jun 13, 2019 at 10:04
    Add a ment  | 

    3 Answers 3

    Reset to default 13

    Javascript handles bitwise operators as signed 32 bit integers.

    Knowing this, if you want to sign extend a byte, you need to propagate the top bit of the byte (which indicates the sign) to all of the higher bits in the thirty two bit integer. This can be achieved with:

    value << 24 >> 24

    What this does is shift the byte to the top of the 32 bit integer, then shift it back down preserving the sign bit.

    Similarly, you can sign extend a 16 bit value with:

    value << 16 >> 16

    This solution converts using 2's plement for negative numbers, which is the standard way negative numbers are encoded.

    function unplement(val, bitwidth) {
    var isnegative = val & (1 << (bitwidth - 1));
    var boundary = (1 << bitwidth);
    var minval = -boundary;
    var mask = boundary - 1;
    return isnegative ? minval + (val & mask) : val;
}

    unplement(0xFF, 8) returns -1
    unplement(0x80, 8) returns -128
    unplement(0x7F, 8) returns 127

    I came up with this solution:

    function convertToSignedInt(signedByte) {
    var sign = signedByte & (1 << 7);
    return (signedByte & 0x7f) * (sign !== 0 ? -1 : 1);
}

    Hope it could save others some time. convertToSignedInt(0x81) // returns -1

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