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 */ 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 */ 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 */ 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