> Not technically a PIC but an ARM Cortex part with a neat built in 32 bit
> CRC calculator.

Here's a 5 instruction ARM implementation of the CRC-CCITT polynomial x^16
+ x^15 + x^5 + 1:

; R0[7:0] = input data, R1[15:0] = input and output crc.
   eor R0,R0,R1 LSR 8  ; R0 = t = (crc0 >> 8) ^ data
   eor R0,R0,R0 LSR 4  ; R0 = t ^ (t >> 4)
   eor R1,R0,R1 LSL 8  ; R1 = (crc0 << 8) ^ t
   eor R1,R1,R0 LSL 5  ; R1 = (crc0 << 8) ^ t ^ (t << 5)
   eor R1,R1,R0 LSL 12 ; R1 = (crc0 << 8) ^ t ^ (t << 5) ^ (t << 12)

It's an implementation of

http://www.dattalo.com/technical/software/pic/crc_1021.asm

I must admit though, I never did test the ARM implementation.

Scott

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