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annotate libgsmefr/enc_lag6.c @ 282:9ee8ad3d4d30

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frtest: rm gsmfr-hand-test and gsmfr-max-out utils These hack programs were never properly documented and were written only as part of a debug chase, in pursuit of a bug that ultimately turned out to be in our then-hacky patch to osmo-bts-sysmo, before beginning of proper patches in Osmocom. These hack programs need to be dropped from the present sw package because they depend on old libgsm, and we are eliminating that dependency.
author Mychaela Falconia <falcon@freecalypso.org>
date Sun, 14 Apr 2024 05:44:47 +0000
parents f151d6c18b31
children
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1 /*************************************************************************
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2 *
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3 * FUNCTION: Enc_lag6
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4 *
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5 * PURPOSE: Encoding of fractional pitch lag with 1/6 resolution.
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6 *
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7 * DESCRIPTION:
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8 * First and third subframes:
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9 * --------------------------
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10 * The pitch range is divided as follows:
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11 * 17 3/6 to 94 3/6 resolution 1/6
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12 * 95 to 143 resolution 1
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13 *
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14 * The period is encoded with 9 bits.
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15 * For the range with fractions:
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16 * index = (T-17)*6 + frac - 3;
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17 * where T=[17..94] and frac=[-2,-1,0,1,2,3]
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18 * and for the integer only range
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19 * index = (T - 95) + 463; where T=[95..143]
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20 *
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21 * Second and fourth subframes:
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22 * ----------------------------
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23 * For the 2nd and 4th subframes a resolution of 1/6 is always used,
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24 * and the search range is relative to the lag in previous subframe.
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25 * If t0 is the lag in the previous subframe then
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26 * t_min=t0-5 and t_max=t0+4 and the range is given by
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27 * (t_min-1) 3/6 to (t_max) 3/6
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28 *
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29 * The period in the 2nd (and 4th) subframe is encoded with 6 bits:
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30 * index = (T-(t_min-1))*6 + frac - 3;
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31 * where T=[t_min-1..t_max] and frac=[-2,-1,0,1,2,3]
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32 *
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33 * Note that only 61 values are used. If the decoder receives 61, 62,
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34 * or 63 as the relative pitch index, it means that a transmission
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35 * error occurred and the pitch from previous subframe should be used.
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36 *
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37 *************************************************************************/
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38
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39 #include "gsm_efr.h"
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40 #include "typedef.h"
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41 #include "namespace.h"
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42 #include "basic_op.h"
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43 #include "no_count.h"
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44 #include "codec.h"
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45
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46 Word16 Enc_lag6 ( /* output: Return index of encoding */
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47 Word16 T0, /* input : Pitch delay */
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48 Word16 *T0_frac, /* in/out: Fractional pitch delay */
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49 Word16 *T0_min, /* in/out: Minimum search delay */
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50 Word16 *T0_max, /* in/out: Maximum search delay */
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51 Word16 pit_min, /* input : Minimum pitch delay */
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52 Word16 pit_max, /* input : Maximum pitch delay */
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53 Word16 pit_flag /* input : Flag for 1st or 3rd subframe */
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54 )
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55 {
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56 Word16 index, i;
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57
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58 test ();
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59 if (pit_flag == 0) /* if 1st or 3rd subframe */
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60 {
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61 /* encode pitch delay (with fraction) */
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62
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63 test ();
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64 if (T0 <= 94)
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65 {
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66 /* index = T0*6 - 105 + *T0_frac */
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67 i = add (add (T0, T0), T0);
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68 index = add (sub (add (i, i), 105), *T0_frac);
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69 } else
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70 { /* set fraction to 0 for delays > 94 */
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71 *T0_frac = 0; move16 ();
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72 index = add (T0, 368);
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73 }
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74
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75 /* find T0_min and T0_max for second (or fourth) subframe */
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76
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77 *T0_min = sub (T0, 5); move16 ();
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78 test ();
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79 if (*T0_min < pit_min)
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80 {
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81 *T0_min = pit_min; move16 ();
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82 }
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83 *T0_max = add (*T0_min, 9);
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84 test ();
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85 if (*T0_max > pit_max)
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86 {
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87 *T0_max = pit_max; move16 ();
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88 *T0_min = sub (*T0_max, 9); move16 ();
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89 }
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90 } else
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91 /* if second or fourth subframe */
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92 {
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93 /* index = 6*(T0-*T0_min) + 3 + *T0_frac */
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94 i = sub (T0, *T0_min);
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95 i = add (add (i, i), i);
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96 index = add (add (add (i, i), 3), *T0_frac);
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97 }
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98
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99 return index;
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100 }