1 /*
2  * Copyright 2022 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 #include <algorithm>
18 #include <math.h>
19 #include <unistd.h>
20 #include "FlowGraphNode.h"
21 #include "Limiter.h"
22 
23 using namespace FLOWGRAPH_OUTER_NAMESPACE::flowgraph;
24 
Limiter(int32_t channelCount)25 Limiter::Limiter(int32_t channelCount)
26         : FlowGraphFilter(channelCount) {
27 }
28 
onProcess(int32_t numFrames)29 int32_t Limiter::onProcess(int32_t numFrames) {
30     const float *inputBuffer = input.getBuffer();
31     float *outputBuffer = output.getBuffer();
32 
33     int32_t numSamples = numFrames * output.getSamplesPerFrame();
34 
35     // Cache the last valid output to reduce memory read/write
36     float lastValidOutput = mLastValidOutput;
37 
38     for (int32_t i = 0; i < numSamples; i++) {
39         // Use the previous output if the input is NaN
40         if (!isnan(*inputBuffer)) {
41             lastValidOutput = processFloat(*inputBuffer);
42         }
43         inputBuffer++;
44         *outputBuffer++ = lastValidOutput;
45     }
46     mLastValidOutput = lastValidOutput;
47 
48     return numFrames;
49 }
50 
processFloat(float in)51 float Limiter::processFloat(float in)
52 {
53     float in_abs = fabsf(in);
54     if (in_abs <= 1) {
55         return in;
56     }
57     float out;
58     if (in_abs < kXWhenYis3Decibels) {
59         out = (kPolynomialSplineA * in_abs + kPolynomialSplineB) * in_abs + kPolynomialSplineC;
60     } else {
61         out = M_SQRT2;
62     }
63     if (in < 0) {
64         out = -out;
65     }
66     return out;
67 }
68