Syntax
CRC(stringA{,stringB}{,ERR=lineref})
Description
The CRC() function returns a 2-byte string containing a special checksum
of stringA. If stringB
is given, it must be 2 bytes long and provide a "seed" for the
checksum. Otherwise, PRO/5 uses a seed of $0000$. CRC() can be used for
verifying data transmissions over communication lines.
Taking the CRC() of a long string that may not fit in memory can be done
one piece at a time because CRC(A$+B$) = CRC(B$,CRC(A$)).
CRC algorithm:
given CRC(A$,B$)
let SEED$=B$ (or $0000$ if B$ not given)
for each byte in A$:
"exclusive or" byte from A$ to low byte of
SEED$
do 8 times:
shift SEED$ one bit to the right
if a 1 bit was shifted out then
exclusive OR $A001$
to SEED$
return(SEED$)
Examples
>LET A$=CRC("NOW IS THE TIME...")
1000 CRC$=CRC(TEXT$,SEED$,ERR=9500)