BigEndian to integer

A bit off topic
Im trying to figure out how to convert BigEndian byte words to integers.
For example ->
0 0 0 18 = 18

The only way I know how to convert this is by writing down on paper, and
writing 8 4 2 1 above the numbers and adding up the values.
Trying to figure out a way via plain old math/php has me stumped at the
moment. (Maybe some sleep is in order)
Any help and or tips would be greatly appreciated.

Thanks

Hello,


This is a reply to an e-mail that you wrote on Mon, 14 Jul 2003 at 09:00,
lines prefixed by '>' were originally written by you.
> A bit off topic
> Im trying to figure out how to convert BigEndian byte words to
> integers.
> For example ->
> 0 0 0 18 = 18
> The only way I know how to convert this is by writing down on paper,
> and
> writing 8 4 2 1 above the numbers and adding up the values.

Never heard of a BigEndian number beofre, but this should do it...

function BigEndiantoInt($bigendian){
$bits = split(" ",$bigendian);
$bits = array_reverse($bits);
$value = 0; $columnvalue = 1;
foreach($bits as $thisbit){
$value = $value + ($columnvalue * $thisbit);
$columnvalue = $columnvalue * 2;
}
return $value;
}

HTH

David

--
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Professional Web Development by David Nicholson
http://www.djnicholson.com/

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(developed entirely in PHP)

> Marek Kilimajer wrote:
> http://www.php.net/pack


A little background on what Im doing. Im attempting to read realaudio
files for their metadata, so Im reading from a binary string,
and Im currently using unpack() (Im new to using this function, so I may
be wrong with its usage) to unpack the data, along with ord(),
and the result is something like what I posted before -> 0 0 0 18 (I
put the spaces in there so we know that each number is a byte)
So Im not exactly sure how the pack() function would play a role in this.

David Nicholson wrote:

>Never heard of a BigEndian number beofre, but this should do it...
>
>function BigEndiantoInt($bigendian){
> $bits = split(" ",$bigendian);
> $bits = array_reverse($bits);
> $value = 0; $columnvalue = 1;
> foreach($bits as $thisbit){
> $value = $value + ($columnvalue * $thisbit);
> $columnvalue = $columnvalue * 2;
> }
> return $value;
>}
>

For taste of what BigEndian or its counterpart LittleEndian is about,
look at ->
http://www.webopedia.com/TERM/B/big_endian.html
http://whatis.techtarget.com/definit...211659,00.html

I'll give your function a shot, and see if I can get something
meaningful from it.
Thanks.

Hi,

Monday, July 14, 2003, 6:00:04 PM, you wrote:
GS> A bit off topic
GS> Im trying to figure out how to convert BigEndian byte words to integers.
For example ->>
GS> 0 0 0 18 = 18

GS> The only way I know how to convert this is by writing down on paper, and
GS> writing 8 4 2 1 above the numbers and adding up the values.
GS> Trying to figure out a way via plain old math/php has me stumped at the
GS> moment. (Maybe some sleep is in order)
GS> Any help and or tips would be greatly appreciated.

GS> Thanks

Here is a simple class that should manipulate bigendian stuff
(untested)

<?php
class bigEndian {
var $data //pointer to data
var $ptr //current position in data
function bigEndian(&$data){
$this->data =& $data;
$this->ptr = 0;
}
function getChar(){
$r = ord($this->data[$this->ptr]);
$this->ptr ++;
return $r;
}
function getWord(){
$r = (ord($this->data[$this->ptr]) << 8) | ord($this->data[$this->ptr+1]);
$this->ptr += 2;
return $r;
}
function getDoubleWord(){
$r = (ord($this->data[$this->ptr]) << 24) | (ord($this->data[$this->ptr+1]) << 16) | (ord($this->data[$this->ptr+2]) << 8) | ord($this->data[$this->ptr+3]);
$this->ptr += 4;
return $r;
}
}

//usage
$datablock = file_get_contents($filename);
$be = new bigEndian($datablock);
$firstword = $be->getWord() //bytes 0,1
$char = $be->getChar() //byte 2
$doubleword = $be->getDoubleWord() //bytes 3,4,5,6
..
..

?>

--
regards,
Tom

Hi,

Tuesday, July 15, 2003, 7:00:33 PM, you wrote:
>> > http://www.php.net/pack
>>
>> A little background on what Im doing. Im attempting to read realaudio
>> files for their metadata, so Im reading from a binary string,
>> and Im currently using unpack() (Im new to using this function, so I may
>> be wrong with its usage) to unpack the data, along with ord(),
>> and the result is something like what I posted before -> 0 0 0 18 (I
>> put the spaces in there so we know that each number is a byte)
>> So Im not exactly sure how the pack() function would play a role in this.

JR> Just in case you're still groggy when you wake up this morning, the page
JR> for pack() lists an 'N' format for unsigned long big endian byte order
JR> for pack() and unpack(). I think what you probably want to do most is
JR> use the 'N' format when you unpack.

JR> (The other responses were amusing, was it a full moon last night? ;-))

JR> --
JR> Joel Rees, permanently jetlagged programmer, Kansai Systems Group
JR> Altech Corporation (Alpsgiken), Osaka, Japan
JR> http://www.alpsgiken.co.jp

Trying to use unpack by itself on large binary streams with variable packet
sizes and content buried in them can become a nightmare. Try to
unscramble an excel file using unpack() :)

--
regards,
Tom

Joel Rees wrote:

>Just in case you're still groggy when you wake up this morning, the page
>for pack() lists an 'N' format for unsigned long big endian byte order
>for pack() and unpack(). I think what you probably want to do most is
>use the 'N' format when you unpack.
>
>(The other responses were amusing, was it a full moon last night? ;-))
>
Thanks for the heads up. Ill give it a try...

Tom Rogers wrote:

>Trying to use unpack by itself on large binary streams with variable packet
>sizes and content buried in them can become a nightmare. Try to
>unscramble an excel file using unpack() :)
>
Yeah, not exactly the most exciting thing to do. As long as I have some
specs on the format, its hasn't been
too bad with mp3 and realaudio files so far...