Andy - Here is the CRC generation function from the version of C-Kermit
I'm working on now (5A).

/* CRC generation tables */

/* LONG means "unsigned long" */

static LONG crcta[16] = { 0L, 010201L, 020402L, 030603L, 041004L,
  051205L, 061406L, 071607L, 0102010L, 0112211L, 0122412L, 0132613L, 0143014L,
  0153215L, 0163416L, 0173617L };

static LONG crctb[16] = { 0L, 010611L, 021422L, 031233L, 043044L,
  053655L, 062466L, 072277L, 0106110L, 0116701L, 0127532L, 0137323L, 0145154L,
  0155745L, 0164576L, 0174367L };


/*  C H K 3  --  Compute a type-3 Kermit block check.  */
/*
 Calculate the 16-bit CRC-CCITT of a null-terminated string using a lookup 
 table.  Assumes the argument string contains no embedded nulls.
*/
unsigned int
chk3(pkt) register CHAR *pkt; {
    register LONG c, crc;
    register unsigned int m;
    m = (parity) ? 0177 : 0377;
    for (crc = 0; *pkt != '\0'; pkt++) {
	c = crc ^ (LONG)(*pkt & m);
	crc = (crc >> 8) ^ (crcta[(c & 0xF0) >> 4] ^ crctb[c & 0x0F]);
    }
    return((unsigned int) (crc & 0xFFFF));
}

And here is a similar routine from DEC-20 Kermit (circa 1985) that shows
the tables in octal, in case that's any help.

; This routine calculates the CRC for a string, using the
; CRC-CCITT polynomial x^16+x^12+x^5+1.
; 
; The string should be the fields of the packet between but not including
; the <mark> and the block check, which is treated as a string of bits with
; the low order bit of the first character first and the high order bit of the
; last character last -- this is how the bits arrive on the transmission line.
; The bit string is divided by the polynomial.
;
; The initial value of the CRC is 0.  The result is the remainder of this
; division, used as-is (i.e. not complemented).
;
; Call with
;  t1/ length of string
;  t2/ 8-bit byte pointer to string
; Returns +1 always, with t1/ 16-bit CRC, t2 unchanged.
;
; AC usage:
;	t1/ Accumulated CRC
;	q4/ Remaining length
;	q3/ Byte pointer to string
;	q2/ temp
;	q1/ temp
;
crcclc:	saveac <q1,q2,q3,q4,t2>	; Save q1-q4, and t2.
	dmove q3,t1		; Get arguments.
	setz t1,		; Initial CRC is 0.
	move t2, parity		;[136] Get parity.

crcc.1:	ildb q1, q4		; Get a character.
	caie t2, none		;[136] Parity = NONE?
	 andi q1, ^o177		;[136] No, doing parity, strip parity bit.
	xori q1, (t1)		; Add in with current CRC.
	ldb q2, [point 4,q1,31]	; Get high 4 bits.
	andi q1, ^o17		; And low 4 bits.
	move q1, crctb2(q1)	; Get low portion of CRC factor.
	xor q1, crctab(q2)	; Plus high portion.
	lsh t1, -^d8		; Shift off a byte from previous CRC.
	xor t1, q1		; Add in new value.
	sojg q3, crcc.1		; Loop for all characters.
	
	ret			; Done, return +1 with CRC in t1.

; Data tables for CRC-CCITT generation

crctab:	oct	0
	oct	10201
	oct	20402
	oct	30603
	oct	41004
	oct	51205
	oct	61406
	oct	71607
	oct	102010
	oct	112211
	oct	122412
	oct	132613
	oct	143014
	oct	153215
	oct	163416
	oct	173617

crctb2:	oct	0
	oct	10611
	oct	21422
	oct	31233
	oct	43044
	oct	53655
	oct	62466
	oct	72277
	oct	106110
	oct	116701
	oct	127532
	oct	137323
	oct	145154
	oct	155745
	oct	164576
	oct	174367