Hi,

Maybe quite strange question and quite off topic, but there's PHP involved

I want to read out files, and then I come across 4byte DWORD values,
they are stored in little endian values, but how do I get in a PHP
string (as the values are too large for integer)

My code is currently this:
$data = fread($fp,4);
$value = (ord(substr($data,3,1))*256*256*256)+(ord(substr($ data,2,1))*256*256)+(ord(substr($data,1,1))*256)+( ord(substr($data,0,1)));

and now $value contains the value of the DWORD, it works fine, but it
seems that it could be done a lot easier
Anyone experience with it?

Tijnema

> -----Original Message-----
> From: Tijnema [private.php?do=newpm&u=]
> Sent: 30 May 2007 15:20
> To: php
> Subject: [PHP] Best way to convert Little-Endian DWORD to string
>
>
> Hi,
>
> Maybe quite strange question and quite off topic, but there's PHP
> involved
>
> I want to read out files, and then I come across 4byte DWORD values,
> they are stored in little endian values, but how do I get in a PHP
> string (as the values are too large for integer)
>
> My code is currently this:
> $data = fread($fp,4);
> $value =
> (ord(substr($data,3,1))*256*256*256)+(ord(substr($ data,2,1))*256*2
> 56)+(ord(substr($data,1,1))*256)+(ord(substr($data ,0,1)));
>
> and now $value contains the value of the DWORD, it works fine, but it
> seems that it could be done a lot easier
> Anyone experience with it?

Could you not use the << bitwise operator?

Edward

On 5/30/07, Edward Kay <EMAIL REMOVED> wrote:
>
>
> > -----Original Message-----
> > From: Tijnema [private.php?do=newpm&u=]
> > Sent: 30 May 2007 15:20
> > To: php
> > Subject: [PHP] Best way to convert Little-Endian DWORD to string
> >
> >
> > Hi,
> >
> > Maybe quite strange question and quite off topic, but there's PHP
> > involved
> >
> > I want to read out files, and then I come across 4byte DWORD values,
> > they are stored in little endian values, but how do I get in a PHP
> > string (as the values are too large for integer)
> >
> > My code is currently this:
> > $data = fread($fp,4);
> > $value =
> > (ord(substr($data,3,1))*256*256*256)+(ord(substr($ data,2,1))*256*2
> > 56)+(ord(substr($data,1,1))*256)+(ord(substr($data ,0,1)));
> >
> > and now $value contains the value of the DWORD, it works fine, but it
> > seems that it could be done a lot easier
> > Anyone experience with it?
>
> Could you not use the << bitwise operator?
>
> Edward

How could I use them here?
I read the docs for bitwise operators, and they tell me what they do,
but now how to use it

Tijnema

On Wed, May 30, 2007 9:19 am, Tijnema wrote:
> Maybe quite strange question and quite off topic, but there's PHP
> involved
>
> I want to read out files, and then I come across 4byte DWORD values,
> they are stored in little endian values, but how do I get in a PHP
> string (as the values are too large for integer)
>
> My code is currently this:
> $data = fread($fp,4);
> $value =
> (ord(substr($data,3,1))*256*256*256)+(ord(substr($ data,2,1))*256*256)+(ord(substr($data,1,1))*256)+( ord(substr($data,0,1)));
>
> and now $value contains the value of the DWORD, it works fine, but it
> seems that it could be done a lot easier
> Anyone experience with it?

Easiest might be to read one byte at a time...

$byte0 = fread($fp, 1);
$byte1 = fread($fp, 1);
$byte2 = fread($fp, 1);
$byte3 = fread($fp, 1);
$value = $byte3 * 0xffffff + $byte2 * 0xffff + $byte1 * 0xff + $byte0;

If that makes fread too slow, which it might, but buffering should be
able to handle 4 bytes...

You could also do:
$byte0 = 0xff000000 & $data;
$byte1 = 0x00ff0000 & $data;
$byte2 = 0x0000ff00 & $data;
$byte3 = 0x000000ff & $data;
//same $value line as above

As far as shifting goes... I *think* this would do it:

$byte3 = $data >> 24;
$byte2 = ($data >> 16) & 0xff;
$byte1 = ($data >> 8) & 0xff;
$byte0 = $data & 0xff;

--
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