[rohc] ROHC-FN tutorial: scaled_seq_no compression formula

[Klaus Warnke <klaus.warnke at acticom.de>]

Hello RoHC'ers 2.0,

the example B.9. in the RFC 4997 ROHC-FN introduces a scaled_seq_no,
but provides no formula for compression. 

Here is my compression formula, maybe it is helpful for other.

scaled_seq_no.UVALUE = (sequence_no.UVALUE + (m*16)) / 3

where m is:

m = 0 if (U%3 == 0)
m = 2 if (U%3 == 1)
m = 1 if (U%3 == 2)

Checked with oo calc:

U	U%3	m	M*16	U+m*16	C=(U+m*16)/3	C*3	U=(C*3)%16
-       ---     -       ----    ------  ------------    ---     ----------
0	0	0	0	0	0	        0	0
1	1	2	32	33	11	        33	1
2	2	1	16	18	6	        18	2
3	0	0	0	3	1	        3	3
4	1	2	32	36	12	        36	4
5	2	1	16	21	7	        21	5
6	0	0	0	6	2	        6	6
7	1	2	32	39	13	        39	7
8	2	1	16	24	8	        24	8
9	0	0	0	9	3	        9	9
10	1	2	32	42	14	        42	10
11	2	1	16	27	9	        27	11
12	0	0	0	12	4	        12	12
13	1	2	32	45	15	        45	13
14	2	1	16	30	10	        30	14
15	0	0	0	15	5	        15	15

br
Klaus