CRCC:   AMSAT CYC2 (x^16 + x^12 + x^5 + 1)   Definition
-------------------------------------------------------

             M             L
            .---------------.
     +--<---| | | | | | | | | DATA
     |      '---------------'
     |
    (+)--------->-----+-------------->------------+-------->--------+
     |                |                           |                 |
     |   .-------.    |    .-------.   .-----.    |    .---------.  |
     +-<-| | | | |<--(+)<--| | | | |<--| | | |<--(+)<--| | | | | |<-+
         '-------'         '-------'   '-----'         '---------'
         <--------- M S B --------->   <--------- L S B --------->

 MSByte sent first, then LSByte.    (+) means "EXOR"

 The initial value of the CRCC register is hex FFFF
 
 Note:  that calculating a crcc of a block that already includes a
 correct crcc as the last 2 last bytes, results in a net crcc = 0
 (Because 16 "0"s are input to the crcc register!)

 This definition is similar to, but NOT the same as, CCITT CRC16

 REM CRCC calculation in BASIC
 REM -------------------------
 crcc%=&FFFF
 FOR i%=0 TO 511
   ch%=buf%?i% << 8 :       REM Get i'th byte; shift left 8 to align with crcc
   FOR j%=0 TO 7
     test% = (ch% EOR crcc%) AND &8000:            REM Do exor; pick out ms bit
     crcc% = crcc% << 1 :                          REM Shift crcc left 1 place
     ch%   =   ch% << 1 :                          REN Shift byte left 1 place
     IF test% <> 0 THEN crcc% = crcc% EOR &1021
   NEXT
 NEXT

 Notes:
   << 8  is equivalent to  * 256
   << 1  is equivalent to  * 2
   &     introduces a hexadecimal number
   %     variables are integers.

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