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comparison libgsmfrp/comfort_noise.c @ 108:3b64f255689a

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libgsmfrp: factor out PRNG into its own module, in preparation for using it as part of speech muting too
author Mychaela Falconia <falcon@freecalypso.org>
date Mon, 28 Nov 2022 04:00:18 +0000
parents 286d5f097eb4
children f081a6850fb5
comparison
equal deleted inserted replaced
107:41f1ae68d253 108:3b64f255689a
15 }; 15 };
16 16
17 static const uint8_t bc[4] = {0, 0, 0, 0}; 17 static const uint8_t bc[4] = {0, 0, 0, 0};
18 static const uint8_t Nc[4] = {40, 120, 40, 120}; 18 static const uint8_t Nc[4] = {40, 120, 40, 120};
19 19
20 /* pseudonoise() function is based on ETSI EFR code */
21
22 static uint16_t pseudonoise(struct gsmfr_preproc_state *st, uint16_t no_bits)
23 {
24 uint16_t noise_bits, Sn, i;
25
26 noise_bits = 0;
27 for (i = 0; i < no_bits; i++)
28 {
29 /* State n == 31 */
30 if ((st->cn_random_lfsr & 0x00000001L) != 0)
31 {
32 Sn = 1;
33 }
34 else
35 {
36 Sn = 0;
37 }
38
39 /* State n == 3 */
40 if ((st->cn_random_lfsr & 0x10000000L) != 0)
41 {
42 Sn = Sn ^ 1;
43 }
44 else
45 {
46 Sn = Sn ^ 0;
47 }
48
49 noise_bits = noise_bits << 1;
50 noise_bits = noise_bits | st->cn_random_lfsr & 1;
51
52 st->cn_random_lfsr >>= 1;
53 if (Sn & 1)
54 {
55 st->cn_random_lfsr |= 0x40000000L;
56 }
57 }
58
59 return noise_bits;
60 }
61
62 static uint8_t random_1to6(struct gsmfr_preproc_state *st) 20 static uint8_t random_1to6(struct gsmfr_preproc_state *st)
63 { 21 {
64 uint8_t range8, range6; 22 uint8_t range8, range6;
65 23
66 range8 = pseudonoise(st, 3); 24 range8 = gsmfr_preproc_prng(st, 3);
67 range6 = fold_table_8to6[(st->cn_random_6fold << 3) | range8]; 25 range6 = fold_table_8to6[(st->cn_random_6fold << 3) | range8];
68 st->cn_random_6fold++; 26 st->cn_random_6fold++;
69 if (st->cn_random_6fold >= 3) 27 if (st->cn_random_6fold >= 3)
70 st->cn_random_6fold = 0; 28 st->cn_random_6fold = 0;
71 return range6; 29 return range6;
80 /* global bytes (magic and LARc) are fixed */ 38 /* global bytes (magic and LARc) are fixed */
81 memcpy(frame, st->sid_prefix, 5); 39 memcpy(frame, st->sid_prefix, 5);
82 c = frame + 5; 40 c = frame + 5;
83 /* now do the 4 subframes, mostly PRNG output */ 41 /* now do the 4 subframes, mostly PRNG output */
84 for (sub = 0; sub < 4; sub++) { 42 for (sub = 0; sub < 4; sub++) {
85 Mc = pseudonoise(st, 2); 43 Mc = gsmfr_preproc_prng(st, 2);
86 for (pulse = 0; pulse < 13; pulse++) 44 for (pulse = 0; pulse < 13; pulse++)
87 xmc[pulse] = random_1to6(st); 45 xmc[pulse] = random_1to6(st);
88 /* packing code from libgsm */ 46 /* packing code from libgsm */
89 *c++ = ((Nc[sub] & 0x7F) << 1) 47 *c++ = ((Nc[sub] & 0x7F) << 1)
90 | ((bc[sub] >> 1) & 0x1); 48 | ((bc[sub] >> 1) & 0x1);