如何在php中将字节数组转换为整数？

Question

I have seen a code that converts integer into byte array . Below is the code on How to convert integer to byte array in php 3 ( How to convert integer to byte array in php ):

<?php

$i = 123456;
$ar = unpack("C*", pack("L", $i));

print_r($ar);
?>

The above code will output:

//output:
Array
(
   [1] => 64
   [2] => 226
   [3] => 1
   [4] => 0
)

But my problem right now is how to reverse this process. Meaning converting from byte array into integer . In the case above, the output will be 123456

Can anybody help me with this. I would be a great help. Thanks ahead.

Answer 1

Why not treat it like the math problem it is?

$i = ($ar[3]<<24) + ($ar[2]<<16) + ($ar[1]<<8) + $ar[0];

Answer 2

Since L is four bytes long, you know the number of elements of the array. Therefore you can simply perform the operation is reverse:

$ar = [64,226,1,0];
$i = unpack("L",pack("C*",$ar[3],$ar[2],$ar[1],$ar[0]));

Answer 3

In order to get a signed 4-byte value in PHP you need to do this:

$temp = ($ar[0]<<24) + ($ar[1]<<16) + ($ar[2]<<8) + ($ar[3]);
if($temp > 2147483648)
     $temp -= 4294967296;