1 /*
2  * Copyright (C) 2015 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 <assert.h>
18 #include <math.h>
19 #include <audio_utils/limiter.h>
20 #include <audio_utils/mono_blend.h>
21 
22 // TODO: Speed up for special case of 2 channels?
23 void mono_blend(void *buf, audio_format_t format, size_t channelCount, size_t frames, bool limit) {
24     if (channelCount < 2) {
25         return;
26     }
27     switch (format) {
28     case AUDIO_FORMAT_PCM_16_BIT: {
29         int16_t *out = (int16_t *)buf;
30         for (size_t i = 0; i < frames; ++i) {
31             const int16_t *in = out;
32             int accum = 0;
33             for (size_t j = 0; j < channelCount; ++j) {
34                 accum += *in++;
35             }
36             accum /= channelCount; // round to 0
37             for (size_t j = 0; j < channelCount; ++j) {
38                 *out++ = accum;
39             }
40         }
41     } break;
42     case AUDIO_FORMAT_PCM_FLOAT: {
43         float *out = (float *)buf;
44         const float recipdiv = 1. / channelCount;
45         for (size_t i = 0; i < frames; ++i) {
46             const float *in = out;
47             float accum = 0;
48             for (size_t j = 0; j < channelCount; ++j) {
49                 accum += *in++;
50             }
51             if (limit && channelCount == 2) {
52                 accum = limiter(accum * M_SQRT1_2);
53             } else {
54                 accum *= recipdiv;
55             }
56             for (size_t j = 0; j < channelCount; ++j) {
57                 *out++ = accum;
58             }
59         }
60     } break;
61     default:
62         assert(false);
63         break;
64     }
65 }
66