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annotate libgsmefr/g_code.c @ 122:b33f2168fdec

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doc/EFR-rationale article written
author Mychaela Falconia <falcon@freecalypso.org>
date Sat, 10 Dec 2022 08:51:01 +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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24
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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 }