        	    Bit packing of SuperFox QPC Messages
-----------------------------------------------------------------------------
The IV3NWV Q-ary Polar Code has parameters (n,k) = (127,50).  The last
three 7-bit information symbols convey a 21-bit CRC based on the first
47 symbols.  Thus, each Super Fox transmission carries a payload of
47*7=329 bits.  On a modern x86 processor the decoder executes in
deterministic time around 5 ms per decode, and always produces a
result.  The CRC test rejects all but around 1 in two million false
decodes.

Bit fields are labeled with tags as defined in the QEX article "The
FT4 and FT8 Communication Protocols" by Franke, Somerville, and Taylor
in QEX for July/August 2020, available on the WSJT web site here:
https://wsjt.sourceforge.io/FT4_FT8_QEX.pdf.  As one example, the tag
'c28' denotes a standard callsign, which requires 28 bits.

=============================================================================
i3 = 0: Standard message: FoxCall, up to 9 HoundCalls, up to 4 signal
reports, "MoreCQs" flag, a digital signature, and a 3-bit message type.
-----------------------------------------------------------------------------
  F  H1  H2  H3  H4  H5  H6  H7  H8  H9 R6 R7 R8 R9   U  Q   D   M      Type
c28 c28 c28 c28 c28 c28 c28 c28 c28 c28 r5 r5 r5 r5  u5 q1 d20  i3=0  Std Msg
                                    280         300 305    326 329
=============================================================================
i3 = 1: If Fox uses a compound callsign we have space for only 8 Hound calls.
Otherwise like type i3=0.
-----------------------------------------------------------------------------
 FC  H1  H2  H2  H4  H5  H6  H7  H8 R5 R6 R7 R8       U  Q   D   M
c58 c28 c28 c28 c28 c28 c28 c28 c28 r5 r5 r5 r5      u3 q1 d20  i3=1
 58                             282         302     305    326 329
=============================================================================
i3 = 2: A free text message with up to 26 characters can be transmitted along
with messages to as many as 4 Hounds conveying either reports or RR73s.
-----------------------------------------------------------------------------
  F  H1  H2  H3  H4 R1 R2 R3 R4           T   T       U  Q   D   M     Type
c28 c28 c28 c28 c28 r5 r5 r5 r5         t71 t71      u3 q1 d20  i3=2  FT+4H
                140         160             302     305    326 329
=============================================================================
i3 = 3: Message "CQ FoxCall Grid <Free text>"
-----------------------------------------------------------------------------
 FC   G   T   T                                       U  Q   D   M      Type
c58 g15 t71 t71                                     u90 q1 d20  i3=3   CQ FT
 58  73 144 215                                     305    326 329
=============================================================================

D  Digital signature (20 bits)
F  Fox call (28 bits)
FC Compound Fox call (58 bits)
G  Grid locator (15 bits)
H  Hound call (28 bits)
M  Message type (3 bits)
Q  MoreCQs flag
R  Report, (5 bits: -18 to +12 dB, or RR73)
T  Free text, up to 26 characters total
U  Unused bits

Unused callsign slots are set to the numerical value for "QU1RKS", and
ignored when received. Similarly for unused t71 slots.  Unused report
slots are set to 0 (-20 dB).  "CQ FoxCall" will be displayed along
with other messages if the "q1" bit is 1.

The SuperFox decoder displays its results with a separate line for each Hound.
Thus, the old-style message "K1ABC RR73; W9XYZ <VP8PJ> -14" becomes

K1ABC VP8PJ RR73
W9XYZ VP8PJ -14
