On 27/11/2017 09:38, Bill Somerville wrote:
On 27/11/2017 03:29, Pete wrote:
On 2017-11-26 8:08 PM, Steven Franke wrote:
Based on these simulations, we determined that the polynomial that
we chose gave excellent performance
What specifically was the polynomial that you tested?
The polynomial being used by WSJTX, as specified to BOOST, is:
x^12 + x^11 + x^10 + x^2 + x
Note that there is no +1 term which should be present in any CRC
polynomial. In effect, what is being used is an eleven bit polynomial:
x^11 + x^10 + x^9 + x + 1
Pete VE5VA
Hi Pete,
boost polynomials for CRC are assumed to have a +1 term, you don't
include it when defining the polynomial to use.
73
Bill
G4WJS.
Hi Pete,
some further details. Boost uses an implied +1 or truncated notation for
good implementation reasons. Shifting the polynomial left by one bit and
assuming that the shifted out bit is always 1 (or eliding the highest
order bit - effectively the same operation) the means that the data
type needed to store the polynomial is never any bigger than the bit
width of the CRC register. So the truncated polynomial 0xc06 used in the
FT8 12-bit CRC is 0x180d (or inverted as 0xb01 (0x1603)) in
non-truncated form, i.e. the forth from last polynomial shown here:
https://users.ece.cmu.edu/~koopman/crc/crc12.html
73
Bill
G4WJS.
------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot
_______________________________________________
wsjt-devel mailing list
wsjt-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/wsjt-devel
