1 /******************************************************************************
2 *
3 * Copyright 2022 Google LLC
4 *
5 * Licensed under the Apache License, Version 2.0 (the "License");
6 * you may not use this file except in compliance with the License.
7 * You may obtain a copy of the License at:
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 *
17 ******************************************************************************/
18
19 #include "plc.h"
20 #include "tables.h"
21
22
23 /**
24 * Reset Packet Loss Concealment state
25 */
lc3_plc_reset(struct lc3_plc_state * plc)26 void lc3_plc_reset(struct lc3_plc_state *plc)
27 {
28 plc->seed = 24607;
29 lc3_plc_suspend(plc);
30 }
31
32 /**
33 * Suspend PLC execution (Good frame received)
34 */
lc3_plc_suspend(struct lc3_plc_state * plc)35 void lc3_plc_suspend(struct lc3_plc_state *plc)
36 {
37 plc->count = 1;
38 plc->alpha = 1.0f;
39 }
40
41 /**
42 * Synthesis of a PLC frame
43 */
lc3_plc_synthesize(enum lc3_dt dt,enum lc3_srate sr,struct lc3_plc_state * plc,const float * x,float * y)44 void lc3_plc_synthesize(enum lc3_dt dt, enum lc3_srate sr,
45 struct lc3_plc_state *plc, const float *x, float *y)
46 {
47 uint16_t seed = plc->seed;
48 float alpha = plc->alpha;
49 int ne = lc3_ne(dt, sr);
50
51 alpha *= (plc->count < 4 ? 1.0f :
52 plc->count < 8 ? 0.9f : 0.85f);
53
54 for (int i = 0; i < ne; i++) {
55 seed = (16831 + seed * 12821) & 0xffff;
56 y[i] = alpha * (seed & 0x8000 ? -x[i] : x[i]);
57 }
58
59 plc->seed = seed;
60 plc->alpha = alpha;
61 plc->count++;
62 }
63
