在 PHP 和 JS 中移位时得到不同的结果

发布于 2024-10-17 04:31:25 字数 821 浏览 3 评论 0原文

我得到一些奇怪的结果，其中 2 个相同的函数（一个在 PHP 中，一个在 javascript 中）返回不同的结果。

这两行代码的输入是相同的：

a = 4653896912;
b = 13;

我仔细检查了变量类型，两个变量在 JS 中都是数字，在 PHP 中都是整数。

PHP 的代码行是这样的：

$a = $a >> $b;

对于 Javascript 来说是这样的：

a = a >> b;

你会期望 a 在两者之后具有相同的值，但我得到以下内容：

PHP: $a = 568102
JS: a = 43814

此时这让我完全困惑。

事实证明，这绝对是 PHP 使用 64 位整数而 JS 仅使用 32 位整数的问题。我现在面临的问题是我需要让 PHP 使用 32 位整数进行这些计算。我发现其他人编写的一个函数看起来应该可以工作，但它似乎根本没有改变我的输出。

private static function toInt32(&$x) {
    $z = hexdec(80000000);
    $y = (int) $x;
    if($y ==- $z && $x <- $z){
        $y = (int) ((-1) * $x);
        $y = (-1) * $y;
    }
    $x = $y;
}

原文

I'm getting some odd results where 2 identical functions (one in PHP and one in javascript) are returning different results.

The input for both of these lines of code is identical:

a = 4653896912;
b = 13;

I have double checked the variable types and both variables are numbers in JS and integers in PHP.

The line of code for PHP is this:

$a = $a >> $b;

For Javascript it's this:

a = a >> b;

You'd expect a to have the same value after both, but I'm getting the following:

PHP: $a = 568102
JS: a = 43814

Which has completely baffled me at this point.

Turns out this is definitely an issue of PHP using 64 bit integers and JS only using 32 bit. The problem I face now is that I need to get PHP to use 32-bit integers for these calculations. I found a function someone else wrote that looks like it should work, but it doesn't seem to be changing the output at all for me.

private static function toInt32(&$x) {
    $z = hexdec(80000000);
    $y = (int) $x;
    if($y ==- $z && $x <- $z){
        $y = (int) ((-1) * $x);
        $y = (-1) * $y;
    }
    $x = $y;
}

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笑咖 2024-10-24 04:31:25

下面的代码演示了屏蔽数字的高 32 位以仅检索低 32 位以在计算中使用。 4294967295 是 2^32 - 1。我认为，如果您以这种方式屏蔽所有可能大于 32 位的值，那么您可以从 php 和 javascript 获得相同的结果。

<?php
    $php_a = 4653896912;
    $php_b = 13;

    //convert $php_a into a 32 bit val
    $php_a = $php_a & 4294967295;

    $a = $php_a >> $php_b;
    echo "PHP: \$a = $a <br />";
?>
<script type="text/javascript">
    var a = 4653896912;
    var b = 13;

    var a = a >> b;
    alert('Javascript A value is ' + a);
</script>

The below code demonstrates masking the upper 32 bits of the number to retrieve only the lower 32 bits to use in your calculations. 4294967295 is 2^32 - 1. I think that if you mask all values that could be greater than 32 bits in this manner, then you can get the same results from your php and javascript.

<?php
    $php_a = 4653896912;
    $php_b = 13;

    //convert $php_a into a 32 bit val
    $php_a = $php_a & 4294967295;

    $a = $php_a >> $php_b;
    echo "PHP: \$a = $a <br />";
?>
<script type="text/javascript">
    var a = 4653896912;
    var b = 13;

    var a = a >> b;
    alert('Javascript A value is ' + a);
</script>

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