How to convert byte array to integer in php?

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.

try to type casting for this.

Yogesh Suthar
– Yogesh Suthar

2012-10-02 02:39:24 +00:00
Commented Oct 2, 2012 at 2:39 — Yogesh Suthar
– Yogesh Suthar, Commented Oct 2, 2012 at 2:39
Possible duplicate of Reverting unpack('C*', "string")

jk2K
– jk2K

2017-12-25 02:05:57 +00:00
Commented Dec 25, 2017 at 2:05 — jk2K
– jk2K, Commented Dec 25, 2017 at 2:05
Here is how to covert byte array into float in PHP.

Syed Azhar Abbas
– Syed Azhar Abbas

2019-06-27 08:13:53 +00:00
Commented Jun 27, 2019 at 8:13 — Syed Azhar Abbas
– Syed Azhar Abbas, Commented Jun 27, 2019 at 8:13

n0099 · Accepted Answer · 2022-12-23 15:40:26Z

11

Why not treat it like the math problem it is?

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

edited Dec 23, 2022 at 15:40

n0099

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answered Oct 2, 2012 at 2:56

PRB

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2 Comments

gchimuel Over a year ago

wow, this solve my problem but I change the code into: $i = ($ar[4]<<24) + ($ar[3]<<16) + ($ar[2]<<8) + ($ar[1]); since $ar[0] doesn't exist and when no parentheses is added between plus sign it will return 0 value. but thanks.

n0099 Over a year ago

@gchimuel The parentheses around last part $ar[0] is unnecessary, other parts is.

Niet the Dark Absol · Accepted Answer · 2012-10-02 02:43:30Z

5

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]));

answered Oct 2, 2012 at 2:43

Niet the Dark Absol

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3 Comments

n0099 Over a year ago

You can also do unpack('L', pack('C*', ...array_reverse($ar))) if you can ensure that $ar have 4 items and being indexed from 0 to 3.

n0099 Over a year ago

Also note the output of unpack('C*', $someBytesArray) will starts index from 1, so you should wrap array_values() on it.

n0099 Over a year ago

The meaning of array_reverse() or writing literal $ar[3], ..., $ar[0] is to convert byte order between big and small endian, if you can ensure the same endian is used through pack() to unpack(), you don't have to reverse them.

n0099 · Accepted Answer · 2022-12-23 17:01:19Z

4

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;

edited Dec 23, 2022 at 17:01

n0099

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answered Mar 5, 2014 at 3:57

ricozinn

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1 Comment

Denis V Over a year ago

Worth to mention that this workaround is needed for x64 builds of PHP (except Windows ones). And there is one mistake in the code. The comparison must be greater or equal instead of just greater.

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