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annotate libgsmefr/g_code.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 9dac98926a2d
children
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1 /*************************************************************************
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2 *
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3 * FUNCTION: G_code
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4 *
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5 * PURPOSE: Compute the innovative codebook gain.
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6 *
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7 * DESCRIPTION:
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8 * The innovative codebook gain is given by
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9 *
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10 * g = <x[], y[]> / <y[], y[]>
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11 *
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12 * where x[] is the target vector, y[] is the filtered innovative
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13 * codevector, and <> denotes dot product.
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14 *
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15 *************************************************************************/
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16
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17 #include "gsm_efr.h"
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18 #include "typedef.h"
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19 #include "namespace.h"
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20 #include "basic_op.h"
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21 #include "no_count.h"
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22 #include "cnst.h"
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23 #include "codec.h"
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25 Word16 G_code ( /* out : Gain of innovation code */
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26 Word16 xn2[], /* in : target vector */
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27 Word16 y2[] /* in : filtered innovation vector */
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28 )
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29 {
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30 Word16 i;
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31 Word16 xy, yy, exp_xy, exp_yy, gain;
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32 Word16 scal_y2[L_SUBFR];
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33 Word32 s;
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34
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35 /* Scale down Y[] by 2 to avoid overflow */
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36
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37 for (i = 0; i < L_SUBFR; i++)
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38 {
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39 scal_y2[i] = shr (y2[i], 1); move16 ();
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40 }
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42 /* Compute scalar product <X[],Y[]> */
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44 s = 1L; move32 (); /* Avoid case of all zeros */
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45 for (i = 0; i < L_SUBFR; i++)
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46 {
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47 s = L_mac (s, xn2[i], scal_y2[i]);
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48 }
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49 exp_xy = norm_l (s);
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50 xy = extract_h (L_shl (s, exp_xy));
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52 /* If (xy < 0) gain = 0 */
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54 test ();
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55 if (xy <= 0)
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56 return ((Word16) 0);
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58 /* Compute scalar product <Y[],Y[]> */
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59
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60 s = 0L; move32 ();
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61 for (i = 0; i < L_SUBFR; i++)
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62 {
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63 s = L_mac (s, scal_y2[i], scal_y2[i]);
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64 }
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65 exp_yy = norm_l (s);
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66 yy = extract_h (L_shl (s, exp_yy));
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68 /* compute gain = xy/yy */
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70 xy = shr (xy, 1); /* Be sure xy < yy */
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71 gain = div_s (xy, yy);
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72
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73 /* Denormalization of division */
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74 i = add (exp_xy, 5); /* 15-1+9-18 = 5 */
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75 i = sub (i, exp_yy);
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77 gain = shr (gain, i);
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78
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79 return (gain);
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80 }