不工作的负输入的无符号右移功能 [英] Unsigned right shift function not working for negative input

问题描述

我正在寻找一种方式来使用＆GT;＆GT;＆GT; 在PHP 5.5.14的64位版本的JavaScript函数。我发现此功能在我的谷歌搜索：

I'm looking for a way to use the >>> function from JavaScript in the 64-bit version of PHP 5.5.14. I found this function in my googling:

function uRShift($a, $b) 
{ 
    $z = hexdec(80000000); 
    if ($z & $a) 
    { 
        $a = ($a >> 1); 
        $a &= (~$z); 
        $a |= 0x40000000; 
        $a = ($a >> ($b - 1)); 
    } else { 
        $a = ($a >> $b); 
    } 
    return $a; 
}

这个功能似乎正数做工精细，但传递负数时，我得到不同的结果。

This function seems to work fine for positive numbers, but I get differing results when passing in negative numbers.

例如：

PHP：

In: echo uRShift(-672461345, 25);
Out: -149

JavaScript的（铬35）：

JavaScript (Chrome 35):

In: -672461345 >>> 25
Out: 107

编辑：

我也试过在上文中提及的答案其它功能。

I also tried the other function mentioned in the answer linked above.

function uRShift($a, $b)
{
    if($b == 0) return $a;
    return ($a >> $b) & ~(1<<(8*PHP_INT_SIZE-1)>>($b-1));
}

PHP：

In: echo uRShift(-672461345, 25);
Out: 549755813867

Runnable接口

推荐答案

恒为0x80000000 （它写成一个呼叫 hexdec 并存储在 $ Z而言变量在这个例子中）再presents最低的补全负整数（ 100000 .. .. 二进制）。这位前pression 〜$ Z而言应该给按位非如此，即最高签署的正整数（这最终被 2147483647 ）。

The constant 0x80000000 (it's written as a call to hexdec and stored in the $z variable in this example) represents the lowest signed two's complement negative integer (100000.... in binary). The expression ~$z should give the bitwise NOT of this, namely, the highest signed positive integer (which ends up being 2147483647).

原来的号码（正 为0x80000000 ，即 2147483648 ）不能存储为签署 32位整数，因此通常将它保存为浮动某​​种。不幸的是，PHP 5.5认为〜（2147483648）等于 -2147483649 ，其中是，如果正确我们处理如： 64位整数的

The original number (positive 0x80000000, that is, 2147483648) cannot be stored as a signed 32-bit integer, so normally it would be stored as a float of some kind. Unfortunately, PHP 5.5 thinks that ~(2147483648) is equal to -2147483649, which would be correct if we were dealing with e.g. 64-bit integers.

事实上，呼应了 PHP_INT_SIZE 在可运行表明整数是8个字节，这是64位。因此，运算不正确的在PHP 5.5的工作了。

And indeed, echoing out PHP_INT_SIZE in runnable indicates that integers are 8 bytes, which is 64 bits. Thus, the arithmetic isn't working out right in PHP 5.5.

要解决这个问题，只需更换〜$ Z而言用静态常量，如下所示：

To remedy this, just replace the ~$z with a static constant, as follows:

function uRShift($a, $b) 
{ 
    if ($a < 0) 
    { 
        $a = ($a >> 1); 
        $a &= 2147483647; 
        $a |= 0x40000000; 
        $a = ($a >> ($b - 1)); 
    } else { 
        $a = ($a >> $b); 
    } 
    return $a; 
}

这功能还是有一定的弱点;例如，通过移0不能正常工作。

This function still has some weaknesses; for example, shifting by 0 doesn't work properly.

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