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comparison libgsmfrp/sidclass.c @ 2:2b5770c715ee

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libgsmfrp: compiling utility functions
author Mychaela Falconia <falcon@freecalypso.org>
date Sat, 19 Nov 2022 07:21:26 +0000
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1:6780b23654bd 2:2b5770c715ee
1 /*
2 * gsmfr_preproc_sid_classify() utility function classifies
3 * a GSM 06.10 frame in RTP encoding according to the rules
4 * of GSM 06.31 (or 3GPP TS 46.031) section 6.1.1, judging it
5 * as SID=0, SID=1 or SID=2.
6 */
7
8 #include "gsm_fr_preproc.h"
9
10 static const unsigned short sid_field_bits[95] = {
11 57, 58, 60, 61, 63, 64, 66, 67, 69, 70, 72, 73,
12 75, 76, 78, 79, 81, 82, 84, 85, 87, 88, 90, 91,
13 93, 94, 113, 114, 116, 117, 119, 120, 122, 123,
14 125, 126, 128, 129, 131, 132, 134, 135, 137,
15 138, 140, 141, 143, 144, 146, 147, 149, 150,
16 169, 170, 172, 173, 175, 176, 178, 179, 181,
17 182, 184, 185, 187, 188, 190, 191, 193, 194,
18 196, 197, 199, 200, 202, 203, 205, 206, 225,
19 226, 228, 229, 231, 232, 234, 235, 237, 240,
20 243, 246, 249, 252, 255, 258, 261
21 };
22
23 static inline int get_bit(const gsm_byte *frame, unsigned bitnum)
24 {
25 unsigned bytenum = bitnum >> 3;
26 unsigned bit_in_byte = 7 - (bitnum & 7);
27 unsigned bitmask = 1 << bit_in_byte;
28
29 if (frame[bytenum] & bitmask)
30 return 1;
31 else
32 return 0;
33 }
34
35 int gsmfr_preproc_sid_classify(const gsm_byte *frame)
36 {
37 unsigned idx, n;
38
39 n = 0;
40 for (idx = 0; idx < 95; idx++) {
41 if (get_bit(frame, sid_field_bits[idx]))
42 n++;
43 if (n >= 16)
44 return 0;
45 }
46 if (n < 2)
47 return 2;
48 else
49 return 1;
50 }