Bugs, features, coding issues

on Tue 06 of Nov., 2018 08:47 CST, by admin2

Thanks to a colleague at ATLAS, a discrepancy between the JANUS reference implementation 'janus-m-3.0.3' and the ANEP-87 document was found.

It affects only packets with cargo of certain lengths.

Taking the Matlab implementation, the interleaver prime computation
function was:

old impelmentation

function prime = interleaver_prime(data_len, k)
    if (nargin < 2)
        k = 5;
    end

    done = 0;

    while done == 0,
        testp = max(primes(k));
        if ((data_len / k < k) && rem(data_len, testp) ~= 0)
            done = 1;
        end
        k = k + 1;
    end

    prime = testp;
end

Where the data block length was compared with the index 'k' and not with
the prime number 'testp' as in the corrected code:

new implementation

function prime = interleaver_prime(data_len, k)
    if (nargin < 2)
        k = 5;
    end

    done = 0;

    while done == 0,
        testp = max(primes(k));
        if ((data_len / testp < testp) && rem(data_len, testp) ~= 0)
            done = 1;
        end
        k = k + 1;
    end

    prime = testp;
end

This problem also affects older versions of C and Matlab implementations.

The corrected version produces an interleaving pattern that is (for some lengths only) incompatible with the one of the previous versions.

Bellow we present a table with cargo lengths up to 256 computed with the old and new methods (consecutive lines with equal values are omitted with the .....).

len	old	corrected
...............
25	7	7
26	5	7
27	5	7
28	5	11
29	5	7
30	7	7
31	5	7
32	5	7
33	5	7
34	5	7
35	11	11
...............
49	11	11
50	7	11
51	7	11
52	7	11
53	7	11
54	7	11
55	7	13
56	11	11
57	7	11
58	7	11
59	7	11
60	7	11
61	7	11
62	7	11
63	11	11
64	7	11
65	7	11
66	7	13
67	7	11
68	7	11
69	7	11
70	11	11
71	7	11
72	7	11
73	7	11
74	7	11
75	7	11
76	7	11
77	13	13
78	7	11
79	7	11
80	7	11
81	7	11
82	7	11
83	7	11
84	11	11
85	7	11
86	7	11
87	7	11
88	7	13
89	7	11
90	7	11
91	11	11
92	7	11
93	7	11
94	7	11
95	7	11
96	7	11
97	7	11
98	11	11
99	7	13
100	11	11
...............
121	13	13
122	11	13
123	11	13
124	11	13
125	11	13
126	11	13
127	11	13
128	11	13
129	11	13
130	11	17
131	11	13
132	13	13
133	11	13
134	11	13
135	11	13
136	11	13
137	11	13
138	11	13
139	11	13
140	11	13
141	11	13
142	11	13
143	17	17
...............
169	17	17
170	13	19
171	13	17
172	13	17
173	13	17
174	13	17
175	13	17
176	13	17
177	13	17
178	13	17
179	13	17
180	13	17
181	13	17
182	17	17
183	13	17
184	13	17
185	13	17
186	13	17
187	13	19
188	13	17
189	13	17
190	13	17
191	13	17
192	13	17
193	13	17
194	13	17
195	17	17
196	13	17
197	13	17
198	13	17
199	13	17
200	13	17
201	13	17
202	13	17
203	13	17
204	13	19
205	13	17
206	13	17
207	13	17
208	17	17
209	13	17
210	13	17
211	13	17
212	13	17
213	13	17
214	13	17
215	13	17
216	13	17
217	13	17
218	13	17
219	13	17
220	13	17
221	19	19
222	13	17
223	13	17
224	13	17
225	13	17
226	13	17
227	13	17
228	13	17
229	13	17
230	13	17
231	13	17
232	13	17
233	13	17
234	17	17
235	13	17
236	13	17
237	13	17
238	13	19
239	13	17
240	13	17
241	13	17
242	13	17
243	13	17
244	13	17
245	13	17
246	13	17
247	17	17
248	13	17
249	13	17
250	13	17
251	13	17
252	13	17
253	13	17
254	13	17
255	13	19
256	17	17

We expect to upload corrected versions of the code soon.

Thank you.

Giovanni

Bugs, features, coding issues

Interleaver prime computation

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