1 /* Copyright 2018 The TensorFlow Authors. All Rights Reserved.
2 
3 Licensed under the Apache License, Version 2.0 (the "License");
4 you may not use this file except in compliance with the License.
5 You may obtain a copy of the License at
6 
7     http://www.apache.org/licenses/LICENSE-2.0
8 
9 Unless required by applicable law or agreed to in writing, software
10 distributed under the License is distributed on an "AS IS" BASIS,
11 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 See the License for the specific language governing permissions and
13 limitations under the License.
14 ==============================================================================*/
15 #ifndef TENSORFLOW_LITE_EXPERIMENTAL_MICROFRONTEND_LIB_FILTERBANK_H_
16 #define TENSORFLOW_LITE_EXPERIMENTAL_MICROFRONTEND_LIB_FILTERBANK_H_
17 
18 #include <stdint.h>
19 #include <stdlib.h>
20 
21 #include "tensorflow/lite/experimental/microfrontend/lib/fft.h"
22 
23 #define kFilterbankBits 12
24 
25 #ifdef __cplusplus
26 extern "C" {
27 #endif
28 
29 struct FilterbankState {
30   int num_channels;
31   int start_index;
32   int end_index;
33   int16_t* channel_frequency_starts;
34   int16_t* channel_weight_starts;
35   int16_t* channel_widths;
36   int16_t* weights;
37   int16_t* unweights;
38   uint64_t* work;
39 };
40 
41 // Converts the relevant complex values of an FFT output into energy (the
42 // square magnitude).
43 void FilterbankConvertFftComplexToEnergy(struct FilterbankState* state,
44                                          struct complex_int16_t* fft_output,
45                                          int32_t* energy);
46 
47 // Computes the mel-scale filterbank on the given energy array. Output is cached
48 // internally - to fetch it, you need to call FilterbankSqrt.
49 void FilterbankAccumulateChannels(struct FilterbankState* state,
50                                   const int32_t* energy);
51 
52 // Applies an integer square root to the 64 bit intermediate values of the
53 // filterbank, and returns a pointer to them. Memory will be invalidated the
54 // next time FilterbankAccumulateChannels is called.
55 uint32_t* FilterbankSqrt(struct FilterbankState* state, int scale_down_shift);
56 
57 void FilterbankReset(struct FilterbankState* state);
58 
59 #ifdef __cplusplus
60 }  // extern "C"
61 #endif
62 
63 #endif  // TENSORFLOW_LITE_EXPERIMENTAL_MICROFRONTEND_LIB_FILTERBANK_H_
64