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annotate libgsmefr/dec_main.c @ 183:452c1d5a6268

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libgsmefr BFI w/o data: emit zero output after decoder reset In real-life usage, each EFR decoder session will most likely begin with lots of BFI frames before the first real frame arrives. However, because the spec-defined home state of the decoder is speech rather than CN, our regular logic for BFI w/o data would have to feed pseudorandom noise to the decoder (in the "fixed codebook excitation pulses" part), which is silly to do at the beginning of the decoder session right out of reset. Therefore, let's check reset_flag_old, and if we are still in the reset state, simply emit zero output.
author Mychaela Falconia <falcon@freecalypso.org>
date Tue, 03 Jan 2023 00:12:18 +0000
parents 18866c0354ef
children
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1 /*
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2 * This module contains our GSM EFR decoder main function, EFR_decode_params(),
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3 * that stands at the boundary between our public interface and the guts of
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4 * ETSI-based codec.
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5 */
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6
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7 #include "gsm_efr.h"
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8 #include "typedef.h"
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9 #include "namespace.h"
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10 #include "basic_op.h"
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11 #include "cnst.h"
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12 #include "codec.h"
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13 #include "sig_proc.h"
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14 #include "memops.h"
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15 #include "dec_state.h"
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16 #include "d_homing.h"
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17
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18 /* These constants define the number of consecutive parameters
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19 that function decoder_homing_frame_test() checks */
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20
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21 #define WHOLE_FRAME 57
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22 #define TO_FIRST_SUBFRAME 18
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23
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24 void EFR_decode_params(struct EFR_decoder_state *st, const int16_t *params,
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25 int bfi, int SID_flag, int TAF, int16_t *pcm_out)
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26 {
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27 Word16 *synth = st->synth_buf + M;
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28 Word16 Az_dec[AZ_SIZE];
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29 Word16 i, temp;
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30 Word16 reset_flag;
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31
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32 if (!bfi) /* BFI == 0, perform DHF check */
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33 {
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34 if (st->reset_flag_old) /* Check for second and further
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35 successive DHF (to first subfr.) */
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36 {
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37 reset_flag = decoder_homing_frame_test (params,
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38 TO_FIRST_SUBFRAME);
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39 }
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40 else
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41 {
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42 reset_flag = 0;
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43 }
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44 }
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45 else /* BFI==1, bypass DHF check (frame
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46 is taken as not being a DHF) */
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47 {
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48 reset_flag = 0;
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49 }
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50
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51 if (reset_flag && st->reset_flag_old)
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52 {
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53 /* Force the output to be the encoder homing frame pattern */
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54
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55 for (i = 0; i < L_FRAME; i++)
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56 {
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57 synth[i] = EHF_MASK;
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58 }
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59 }
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60 else
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61 {
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62 /* Synthesis */
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63 Decoder_12k2 (st, bfi, params, synth, Az_dec, TAF, SID_flag);
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64
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65 Post_Filter (st, synth, Az_dec); /* Post-filter */
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66
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67 for (i = 0; i < L_FRAME; i++)
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68 /* Upscale the 15 bit linear PCM to 16 bits,
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69 then truncate to 13 bits */
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70 {
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71 temp = shl (synth[i], 1);
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72 synth[i] = temp & 0xfff8;
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73 }
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74 } /* else */
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75
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76 Copy (synth, pcm_out, L_FRAME);
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77
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78 /* BFI == 0, perform check for first DHF (whole frame) */
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79 if (!bfi && !st->reset_flag_old)
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80 {
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81 reset_flag = decoder_homing_frame_test (params, WHOLE_FRAME);
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82 }
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83
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84 if (reset_flag)
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85 {
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86 /* Bring the decoder and receive DTX to the home state */
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87 EFR_decoder_reset(st);
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88 } else {
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89 st->reset_flag_old = 0;
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90 }
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91 }