Does anybody recognise this checksum?

Just out of curiosity this really, I found this checksum algorithm by a bit of reverse engineering of some old network code, it was being used to check UDP datagrams. I wondered if some of the more experienced coders here might recognise it as a standard algorithm, or whether it's proprietory?

Code:

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u16 GetChecksum(BYTE data[], u16 datalength){
        unsigned int bytesum=0;
        unsigned int cumulativebytesum=0;
        for(int i = datalength; i>0; i--){
                bytesum+=data[i-1];
                if(bytesum>0xFF) bytesum-=0xFF;
                cumulativebytesum+=bytesum;
        }
        BYTE remainder = cumulativebytesum%0xFF;
        remainder = (remainder+bytesum)%0xFF;
        BYTE byte1 = 0xFF-remainder;
        BYTE byte2 = 0xFF-(byte1+bytesum)%0xFF;
        return 0x100*byte1+byte2;
}

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