#This is an awk program to get checksums for the Magellan GPS
#strings.  Execute "awk -f getchecksum.awk" and enter your 
#favorite Magellan command to get its 
#"byte-wise exclusive OR of allbytes in the message" checksum.  
#
#B.D.D. 15 January 2002

# ord.awk -- do ord and chr
# Global identifiers:
#    _ord_:        numerical values indexed by characters
#    _ord_init:    function to initialize _ord_
BEGIN    { _ord_init() }

function _ord_init(    low, high, i, t)
{
    low = sprintf("%c", 7) # BEL is ascii 7
    if (low == "\a") {    # regular ascii
        low = 0
        high = 127
    } else if (sprintf("%c", 128 + 7) == "\a") {
        # ascii, mark parity
        low = 128
        high = 255
    } else {        # ebcdic(!)
        low = 0
        high = 255
    }
    

    for (i = low; i <= high; i++) {
        t = sprintf("%c", i)
        _ord_[t] = i
    }
}


function ord(str,    c)
{
    # only first character is of interest
    c = substr(str, 1, 1)
    return _ord_[c]
}

function chr(c)
{
    # force c to be numeric by adding 0
    return sprintf("%c", c + 0)
}

#### test code ####
 BEGIN    \
 {
    for (;;) {
        printf("enter a string: ")
        if (getline var <= 0)
            break
        L=length(var)
        C = 0
        i = 1
        while ( i <= L ) {
        B = substr(var, i, 1) 
        B=ord(B)
        C = xor(C,B)
        i = i + 1
    }
printf("%x \n",C)

    }
 }