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/******************************************************************************
*
* Copyright 2022 Google LLC
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at:
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
******************************************************************************/
#include "plc.h"
#include "tables.h"
/**
* Reset Packet Loss Concealment state
*/
void lc3_plc_reset(struct lc3_plc_state *plc)
{
plc->seed = 24607;
lc3_plc_suspend(plc);
}
/**
* Suspend PLC execution (Good frame received)
*/
void lc3_plc_suspend(struct lc3_plc_state *plc)
{
plc->count = 1;
plc->alpha = 1.0f;
}
/**
* Synthesis of a PLC frame
*/
void lc3_plc_synthesize(enum lc3_dt dt, enum lc3_srate sr,
struct lc3_plc_state *plc, const float *x, float *y)
{
uint16_t seed = plc->seed;
float alpha = plc->alpha;
int ne = lc3_ne(dt, sr);
alpha *= (plc->count < 4 ? 1.0f :
plc->count < 8 ? 0.9f : 0.85f);
for (int i = 0; i < ne; i++) {
seed = (16831 + seed * 12821) & 0xffff;
y[i] = alpha * (seed & 0x8000 ? -x[i] : x[i]);
}
plc->seed = seed;
plc->alpha = alpha;
plc->count++;
}
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