Why left shift is different between PHP and Javascript

Question

In Javascript

p = 105874240;
105874240
p << 5;
-906991616

But in PHP

php > echo $p = 105874240;
105874240
php > echo $p << 5;
3387975680

I search some introduce about the different, because Javascript use signed int32. But I can't find the right solution for it, all not work for me.

Could you please tell me what's going on, and how can I get the same result of Javascript in PHP. Thank you.

Take a look at this stackoverflow.com/questions/1908492/… you need to use the >>> operator to convert to 32bit unsigned int in js. — steven
– steven, Commented Feb 11, 2017 at 8:55
I mean Javascript result is right, I want PHP get the same result, not change the Javascipt. — Tony Gao
– Tony Gao, Commented Feb 11, 2017 at 8:58
Do you know the difference(s) between signed and unsigned integers and how to tell the OS which one to use and when? — Mjh
– Mjh, Commented Feb 11, 2017 at 10:11

GOTO 0 · Accepted Answer · 2017-02-11 09:00:33Z

2

This is how I'd do it.

function to32bits($value)
{
    $value = ($value & 0xffffffff);
    if ($value & 0x80000000) $value = -((~$value & 0xffffffff) + 1);
    return $value;
}

$p = 105874240;
echo to32bits($p << 5); // -906991616

answered Feb 11, 2017 at 9:00

GOTO 0

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