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
21
22 /**
23 * Reset Packet Loss Concealment state
24 */
lc3_plc_reset(struct lc3_plc_state * plc)25 void lc3_plc_reset(struct lc3_plc_state *plc)
26 {
27 plc->seed = 24607;
28 lc3_plc_suspend(plc);
29 }
30
31 /**
32 * Suspend PLC execution (Good frame received)
33 */
lc3_plc_suspend(struct lc3_plc_state * plc)34 void lc3_plc_suspend(struct lc3_plc_state *plc)
35 {
36 plc->count = 1;
37 plc->alpha = 1.0f;
38 }
39
40 /**
41 * Synthesis of a PLC frame
42 */
lc3_plc_synthesize(enum lc3_dt dt,enum lc3_srate sr,struct lc3_plc_state * plc,const float * x,float * y)43 void lc3_plc_synthesize(enum lc3_dt dt, enum lc3_srate sr,
44 struct lc3_plc_state *plc, const float *x, float *y)
45 {
46 uint16_t seed = plc->seed;
47 float alpha = plc->alpha;
48 int ne = LC3_NE(dt, sr);
49
50 alpha *= (plc->count < 4 ? 1.0f :
51 plc->count < 8 ? 0.9f : 0.85f);
52
53 for (int i = 0; i < ne; i++) {
54 seed = (16831 + seed * 12821) & 0xffff;
55 y[i] = alpha * (seed & 0x8000 ? -x[i] : x[i]);
56 }
57
58 plc->seed = seed;
59 plc->alpha = alpha;
60 plc->count++;
61 }
62
