[Octave-bug-tracker] [bug #60800] (communications) rsenc() returns incorrect result with shortened messages

[anonymous]

URL:
  <https://savannah.gnu.org/bugs/?60800>

                 Summary: (communications) rsenc() returns incorrect result
with shortened messages
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Sun 20 Jun 2021 12:46:45 AM UTC
                Category: Libraries
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: Matt Hostetter
        Originator Email: matthostetter@gmail.com
             Open/Closed: Open
                 Release: 5.2.0
         Discussion Lock: Any
        Operating System: GNU/Linux

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Details:

Reed-Solomon encoding with shortened codes seems to not be working.

The generator polynomial for RS(15, 9) is g(x) = x^6 + 7x^5 + 9x^4 + 3x^3 +
12x^2 + 10x + 12. Encoding the message m(x) = 1 should result in the codeword
c(x) = m(x)g(x) = g(x), as seen in the third line. However, when encoding the
shortened message [0,0,0,0,1] the incorrect codeword is produced.


octave:165> rsgenpoly(15, 9)
ans =
GF(2^4) array. Primitive Polynomial = D^4+D+1 (decimal 19)

Array elements = 

    1    7    9    3   12   10   12

octave:166> rsenc(gf([0,0,0,0,1], 4), 15-4, 9-4, 'end')
ans =
GF(2^4) array. Primitive Polynomial = D^4+D+1 (decimal 19)

Array elements = 

    0    0    0    0    1    7    1   12    8   10   12

octave:167> rsenc(gf([0,0,0,0,0,0,0,0,1], 4), 15, 9, 'end')
ans =
GF(2^4) array. Primitive Polynomial = D^4+D+1 (decimal 19)

Array elements = 

    0    0    0    0    0    0    0    0    1    7    9    3   12   10   12





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