[avr-libc-dev] [patch #3925] Dallas iButton 8-bit CRC

[anonymous]

URL:
  <http://savannah.nongnu.org/patch/?func=detailitem&item_id=3925>

                 Summary: Dallas iButton 8-bit CRC
                 Project: AVR C Runtime Library
            Submitted by: None
            Submitted on: Wed 04/20/05 at 21:32
                Category: None
                Priority: 2
                  Status: None
                 Privacy: Public
             Assigned to: None
        Originator Email: 
             Open/Closed: Open

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Details:

I couldn't find this when I went looking for it. So I modified the example in
the crc_xmodem_update function, to come up with the following code. This saved
me 252 bytes vs. a lookup table. I don't know if this CRC is too specific to
this application to be included in this project or not, but here it is
anyways. Maybe it will help someone.

uint8_t crc_ibutton_update (uint8_t crc, uint8_t data)
{
        char i;

        crc = crc ^ data;
        for (i=0; i<8; i++)
        {
                if (crc & 0x01)
                        crc = (crc >> 1) ^ 0x8C;
                else
                        crc >>= 1;
        }

        return crc;
}






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