'IF YOU ARE LOOKING AT THIS WITH A BROWSER, USE THE BACK BUTTON TO GET
' BACK TO THE PREVIOUS PAGE. YOU CAN ALSO DOWNLOAD THIS FILE BY GOING
' BACK AND RIGHT CLICKING ON THE LINK, THEN SELECTING THE APPROPRIATE
' COMMAND.

' Calculates the checksum and crc (as defined by SAE)
' for a string of numbers

CLS
DIM buf%(12)
begin:
INPUT "Number of bytes"; nbytes%
FOR i% = 1 TO nbytes%
PRINT "Enter number"; i%; " ";
INPUT buf%(i%)
NEXT i%

GOSUB ErrByte
PRINT "CRC=       "; HEX$(CRC%); " hex      "; CRC%; "dec"
PRINT "Checksum=  "; HEX$(checksum%); " hex      "; checksum%; "dec"
PRINT
GOTO begin

ErrByte:
checksum% = 0
CrcReg% = 255
FOR i% = 1 TO nbytes%
BitPoint% = 128
Byte% = buf%(i%)

FOR j% = 0 TO 7
IF BitPoint% AND Byte% THEN
        IF CrcReg% AND 128 THEN Poly% = 1 ELSE Poly% = 28
        CrcReg% = (((CrcReg% * 2) OR 1) XOR Poly%) AND 255
ELSE
        IF (CrcReg% AND 128) THEN Poly% = 29 ELSE Poly% = 0
        CrcReg% = ((CrcReg% * 2) XOR Poly%) AND 255
END IF
BitPoint% = BitPoint% \ 2
NEXT j%
checksum% = (checksum% + Byte%) AND 255
NEXT i%
CRC% = (NOT CrcReg%) AND 255
RETURN