You Can think of

  *p++

as  func(p) where func is defined as:

  int func(p)
  {

    int temp;       // assuming p is a pointer to int

    temp = *p;      // save the value pointed by pointer p
    p++;            // add to p the size in bytes of the items it points to
    return temp
  }


In C, p++ takes the value and then increment, ++p increments and then take
the
value.

Tal

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Pang
> Sent: Sunday, May 05, 2002 7:40 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [OT]:Question on CRC ( based on notes by Ross Williams )
>
>
> Hi all,
>
> I am currently reading some notes with the title 'CRC primer by Ross
> Williams'. I am stuck at section 9-A table driven implementation.
> Wondering
> if anyone has gone through the same notes and hopefully provide me some
> guidance.
> The link for the notes are as below - www.riccibitti.com/crcguide.htm
>
> I do not understand what the C codes trying to do -
>
> r = 0;
> while ( len-- )
> {
>     byte t = ( r >> 24 ) & 0xFF;
>     r = ( r << 8 )  | *p++;             // why OR with the contents of the
> address pointer?
>     r^ =table[t];
> }
>
> where r = register, len = length of the message, t = temporary?,
> p = points
> to the augmented message
>
> I understand roughly the table way of implementation, but in the
> code above,
> r was not loaded with a new value, so how does the bytes move on?
>
> I will be gratefull for any guidance given.
>
> Rgds,
>
> Pang
>
> --
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>
>

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