path: root/audio_resampler.c (plain)
blob: 78868248fc3d606343ea54d316e42a544b3d7175

1	#include <math.h>
2	#include <cutils/log.h>
3
4	#include "audio_resampler.h"
5
6	#define LOG_TAG "usb_audio_resampler"
7
8	//Clip from 16.16 fixed-point to 0.15 fixed-point.
9	inline static short clip(int x) {
10	if (x < -32768) {
11	return -32768;
12	} else if (x > 32767) {
13	return 32767;
14	} else {
15	return x;
16	}
17	}
18
19	int resampler_init(struct resample_para *resample) {
20
21	ALOGD("%s, Init Resampler: input_sr = %d, output_sr = %d \n",
22	__FUNCTION__,resample->input_sr,resample->output_sr);
23
24	static const double kPhaseMultiplier = 1L << 28;
25
26	resample->FractionStep = (unsigned int) (resample->input_sr * kPhaseMultiplier
27	/ resample->output_sr);
28	resample->SampleFraction = 0;
29	resample->lastsample_left = 0;
30	resample->lastsample_right = 0;
31	return 0;
32	}
33
34	int resample_process(struct resample_para *resample, unsigned int in_frame,
35	short* input, short* output) {
36	unsigned int inputIndex = 0;
37	unsigned int outputIndex = 0;
38	unsigned int FractionStep = resample->FractionStep;
39
40	static const unsigned int kPhaseMask = (1LU << 28) - 1;
41	unsigned int frac = resample->SampleFraction;
42	short lastsample_left = resample->lastsample_left;
43	short lastsample_right = resample->lastsample_right;
44
45	if(resample->channels == 2){
46	while (inputIndex == 0) {
47	*output++ = clip((int) lastsample_left +
48	((((int) input[0] - (int) lastsample_left) * ((int) frac >> 13)) >> 15));
49	*output++ = clip((int) lastsample_right +
50	((((int) input[1] - (int) lastsample_right) * ((int) frac >> 13)) >> 15));
51
52	frac += FractionStep;
53	inputIndex += (frac >> 28);
54	frac = (frac & kPhaseMask);
55	outputIndex++;
56	}
57
58	while (inputIndex < in_frame) {
59	*output++ = clip((int) input[2 * inputIndex - 2] + ((((int) input[2 * inputIndex]
60	- (int) input[2 * inputIndex - 2]) * ((int) frac >> 13)) >> 15));
61	*output++ = clip((int) input[2 * inputIndex - 1] + ((((int) input[2 * inputIndex + 1]
62	- (int) input[2 * inputIndex - 1]) * ((int) frac >> 13)) >> 15));
63
64	frac += FractionStep;
65	inputIndex += (frac >> 28);
66	frac = (frac & kPhaseMask);
67	outputIndex++;
68	}
69
70	resample->lastsample_left = input[2 * in_frame - 2];
71	resample->lastsample_right = input[2 * in_frame - 1];
72	resample->SampleFraction = frac;
73	}else{
74	//left channel as output
75	while (inputIndex == 0) {
76	*output++ = clip((int) lastsample_left +
77	((((int) input[0] - (int) lastsample_left) * ((int) frac >> 13)) >> 15));
78
79	frac += FractionStep;
80	inputIndex += (frac >> 28);
81	frac = (frac & kPhaseMask);
82	outputIndex++;
83	}
84
85	while (inputIndex < in_frame) {
86	*output++ = clip((int) input[2 * inputIndex - 2] + ((((int) input[2 * inputIndex]
87	- (int) input[2 * inputIndex - 2]) * ((int) frac >> 13)) >> 15));
88
89	frac += FractionStep;
90	inputIndex += (frac >> 28);
91	frac = (frac & kPhaseMask);
92	outputIndex++;
93	}
94
95	resample->lastsample_left = input[2 * in_frame - 2];
96	resample->SampleFraction = frac;
97	}
98
99	return outputIndex;
100	}
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104