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comparison libgsmefr/dec_lag6.c @ 53:49dd1ac8e75b

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libgsmefr: import most *.c files from ETSI source
author Mychaela Falconia <falcon@freecalypso.org>
date Fri, 25 Nov 2022 16:18:21 +0000
parents
children cb080ec1817e
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52:988fd7ff514f 53:49dd1ac8e75b
1 /*************************************************************************
2 * FUNCTION: Dec_lag6
3 *
4 * PURPOSE: Decoding of fractional pitch lag with 1/6 resolution.
5 * Extract the integer and fraction parts of the pitch lag from
6 * the received adaptive codebook index.
7 *
8 * See "Enc_lag6.c" for more details about the encoding procedure.
9 *
10 * The fractional lag in 1st and 3rd subframes is encoded with 9 bits
11 * while that in 2nd and 4th subframes is relatively encoded with 6 bits.
12 * Note that in relative encoding only 61 values are used. If the
13 * decoder receives 61, 62, or 63 as the relative pitch index, it means
14 * that a transmission error occurred. In this case, the pitch lag from
15 * previous subframe is used.
16 *
17 *************************************************************************/
18
19 #include "typedef.h"
20 #include "basic_op.h"
21 #include "count.h"
22
23 /* Old integer lag */
24
25 Word16 old_T0;
26
27 Word16
28 Dec_lag6 ( /* output: return integer pitch lag */
29 Word16 index, /* input : received pitch index */
30 Word16 pit_min, /* input : minimum pitch lag */
31 Word16 pit_max, /* input : maximum pitch lag */
32 Word16 i_subfr, /* input : subframe flag */
33 Word16 L_frame_by2,/* input : speech frame size divided by 2 */
34 Word16 *T0_frac, /* output: fractional part of pitch lag */
35 Word16 bfi /* input : bad frame indicator */
36 )
37 {
38 Word16 pit_flag;
39 Word16 T0, i;
40 static Word16 T0_min, T0_max;
41
42 pit_flag = i_subfr; move16 (); /* flag for 1st or 3rd subframe */
43 test ();
44 if (sub (i_subfr, L_frame_by2) == 0)
45 {
46 pit_flag = 0; move16 ();
47 }
48 test ();
49 if (pit_flag == 0) /* if 1st or 3rd subframe */
50 {
51 test ();
52 if (bfi == 0)
53 { /* if bfi == 0 decode pitch */
54 test ();
55 if (sub (index, 463) < 0)
56 {
57 /* T0 = (index+5)/6 + 17 */
58 T0 = add (mult (add (index, 5), 5462), 17);
59 i = add (add (T0, T0), T0);
60 /* *T0_frac = index - T0*6 + 105 */
61 *T0_frac = add (sub (index, add (i, i)), 105);
62 move16 ();
63 }
64 else
65 {
66 T0 = sub (index, 368);
67 *T0_frac = 0; move16 ();
68 }
69 }
70 else
71 /* bfi == 1 */
72 {
73 T0 = old_T0; move16 ();
74 *T0_frac = 0; move16 ();
75 }
76
77 /* find T0_min and T0_max for 2nd (or 4th) subframe */
78
79 T0_min = sub (T0, 5);
80 test ();
81 if (sub (T0_min, pit_min) < 0)
82 {
83 T0_min = pit_min; move16 ();
84 }
85 T0_max = add (T0_min, 9);
86 test ();
87 if (sub (T0_max, pit_max) > 0)
88 {
89 T0_max = pit_max; move16 ();
90 T0_min = sub (T0_max, 9);
91 }
92 }
93 else
94 /* second or fourth subframe */
95 {
96 test (); test ();
97 /* if bfi == 0 decode pitch */
98 if ((bfi == 0) && (sub (index, 61) < 0))
99 {
100 /* i = (index+5)/6 - 1 */
101 i = sub (mult (add (index, 5), 5462), 1);
102 T0 = add (i, T0_min);
103 i = add (add (i, i), i);
104 *T0_frac = sub (sub (index, 3), add (i, i));
105 move16 ();
106 }
107 else
108 /* bfi == 1 OR index >= 61 */
109 {
110 T0 = old_T0; move16 ();
111 *T0_frac = 0; move16 ();
112 }
113 }
114
115 old_T0 = T0; move16 ();
116
117 return T0;
118 }