pack

If you'd like to understand pack/unpack. There is a tutorial here in perl, that works equally well in understanding it for php:http://perldoc.perl.org/perlpacktut.html

A helper class to convert integer to binary strings and vice versa. Useful for writing and reading integers to / from files or sockets.<?php    class int_helper    {        public static function int8($i) {            return is_int($i) ? pack("c", $i) : unpack("c", $i)[1];        }        public static function uInt8($i) {            return is_int($i) ? pack("C", $i) : unpack("C", $i)[1];        }        public static function int16($i) {            return is_int($i) ? pack("s", $i) : unpack("s", $i)[1];        }        public static function uInt16($i, $endianness=false) {            $f = is_int($i) ? "pack" : "unpack";            if ($endianness === true) {  // big-endian                $i = $f("n", $i);            }            else if ($endianness === false) {  // little-endian                $i = $f("v", $i);            }            else if ($endianness === null) {  // machine byte order                $i = $f("S", $i);            }            return is_array($i) ? $i[1] : $i;        }        public static function int32($i) {            return is_int($i) ? pack("l", $i) : unpack("l", $i)[1];        }        public static function uInt32($i, $endianness=false) {            $f = is_int($i) ? "pack" : "unpack";            if ($endianness === true) {  // big-endian                $i = $f("N", $i);            }            else if ($endianness === false) {  // little-endian                $i = $f("V", $i);            }            else if ($endianness === null) {  // machine byte order                $i = $f("L", $i);            }            return is_array($i) ? $i[1] : $i;        }        public static function int64($i) {            return is_int($i) ? pack("q", $i) : unpack("q", $i)[1];        }        public static function uInt64($i, $endianness=false) {            $f = is_int($i) ? "pack" : "unpack";            if ($endianness === true) {  // big-endian                $i = $f("J", $i);            }            else if ($endianness === false) {  // little-endian                $i = $f("P", $i);            }            else if ($endianness === null) {  // machine byte order                $i = $f("Q", $i);            }            return is_array($i) ? $i[1] : $i;        }    }?>Usage example:<?php    Header("Content-Type: text/plain");    include("int_helper.php");    echo int_helper::uInt8(0x6b) . PHP_EOL;  // k    echo int_helper::uInt8(107) . PHP_EOL;  // k    echo int_helper::uInt8("\x6b") . PHP_EOL . PHP_EOL;  // 107    echo int_helper::uInt16(4101) . PHP_EOL;  // \x05\x10    echo int_helper::uInt16("\x05\x10") . PHP_EOL;  // 4101    echo int_helper::uInt16("\x05\x10", true) . PHP_EOL . PHP_EOL;  // 1296    echo int_helper::uInt32(2147483647) . PHP_EOL;  // \xff\xff\xff\x7f    echo int_helper::uInt32("\xff\xff\xff\x7f") . PHP_EOL . PHP_EOL;  // 2147483647    // Note: Test this with 64-bit build of PHP    echo int_helper::uInt64(9223372036854775807) . PHP_EOL;  // \xff\xff\xff\xff\xff\xff\xff\x7f    echo int_helper::uInt64("\xff\xff\xff\xff\xff\xff\xff\x7f") . PHP_EOL . PHP_EOL;  // 9223372036854775807?>

Note that the the upper command in perl looks like this:

$binarydata = pack ("n v c*", 0x1234, 0x5678, 65, 66);
In PHP it seems that no whitespaces are allowed in the first parameter. So if you want to convert your pack command from perl -> PHP, don't forget to remove the whitespaces!

If you need to unpack a signed short from big-endian or little-endian specifically, instead of machine-byte-order, you need only unpack it as the unsigned form, and then if the result is >= 2^15, subtract 2^16 from it.

And example would be:

<?php
$foo = unpack("n", $signedbigendianshort);
$foo = $foo[1];
if($foo >= pow(2, 15)) $foo -= pow(2, 16);
?>

/* Convert float from HostOrder to Network Order */function FToN( $val ){    $a = unpack("I",pack( "f",$val ));    return pack("N",$a[1] );}    /* Convert float from Network Order to HostOrder */function NToF($val ){    $a = unpack("N",$val);    $b = unpack("f",pack( "I",$a[1]));    return $b[1];}

Be aware of format code H always padding the 0 for byte-alignment to the right (for odd count of nibbles).So pack("H", "7") results in 0x70 (ASCII character 'p') and not in 0x07 (BELL character)as well as pack("H*", "347") results in 0x34 ('4') and 0x70 ('p') and not 0x03 and 0x47.

You will get the same effect with<?phpfunction _readInt($fp){   return unpack('V', fread($fp, 4));}?>or unpack('N', ...) for big-endianness.

Even though in a 64-bit architecure intval(6123456789) = 6123456789, and sprintf('%b', 5000000000) = 100101010000001011111001000000000
pack will not treat anything passed to it as 64-bit.  If you want to pack a 64-bit integer:

<?php
$big = 5000000000;

$left = 0xffffffff00000000;
$right = 0x00000000ffffffff;

$l = ($big & $left) >>32;
$r = $big & $right;

$good = pack('NN', $l, $r);

$urlsafe = str_replace(array('+','/'), array('-','_'), base64_encode($good));

//done!

//rebuild:
$unurl =  str_replace(array('-','_'), array('+','/'), $urlsafe);
$binary = base64_decode($unurl);

$set = unpack('N2', $tmp);
print_r($set);

$original = $set[1] << 32 | $set[2];
echo $original, "\\r\\n";
?>

results in:
Array
(
    [1] => 1
    [2] => 705032704
)
5000000000

but ONLY on a 64-bit enabled machine and PHP distro.

pack()h    Hex string, low nibble first (not same hex2bin())H    Hex string, high nibble first (same hex2bin())

Using pack to write Arabic char(s) to a file.<?php$text = "&#13574;&#13830;&#13830;";$text = mb_convert_encoding($text, "UCS-2BE", "HTML-ENTITIES");$len =  mb_strlen($text);$bom = mb_convert_encoding("&#65534;", "unicode", "HTML-ENTITIES");$fp = fopen('text.txt', 'w');fwrite($fp, pack('a2', $bom));  fwrite($fp, pack("a{$len}", $text));fwrite($fp, pack('a2', $bom)); fwrite($fp, pack('a2', "\n"));fclose($fp);?>