/*

Teamsound data CRC algorithm 0.1
by Luigi Auriemma
e-mail: aluigi@autistici.org
web:    aluigi.org

This simple algorithm calculates the 16 bit checksum stored at the end
(the last 4 bytes) of each data block of the program Teamsound
(http://www.teamsound.com).

To use it:

  crc = teamsound_cksum(data_block, data_block_size);

*/

unsigned short teamsound_cksum(unsigned char *data, int fullsize) {
    int             cksum = 0;
    unsigned short  *ptr;

    if(fullsize <= 4) return(0x0000);
    ptr = (unsigned short *)data;
    fullsize = (fullsize - 4) >> 1;
    while(fullsize--) {
        cksum += *ptr;              // add dx, ax
        if(cksum > 0xffff) cksum++; // adc dx, 00
        cksum &= 0xffff;            // I don't know other methods
        ptr++;                      // to do "adc" in C
    }
    cksum = (cksum >> 8) | (cksum << 8);
    return(cksum);
}