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comparison libgsmefr/lsp_az.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 5bc228bb421e
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52:988fd7ff514f 53:49dd1ac8e75b
1 /*************************************************************************
2 *
3 * FUNCTION: Lsp_Az
4 *
5 * PURPOSE: Converts from the line spectral pairs (LSP) to
6 * LP coefficients, for a 10th order filter.
7 *
8 * DESCRIPTION:
9 * - Find the coefficients of F1(z) and F2(z) (see Get_lsp_pol)
10 * - Multiply F1(z) by 1+z^{-1} and F2(z) by 1-z^{-1}
11 * - A(z) = ( F1(z) + F2(z) ) / 2
12 *
13 *************************************************************************/
14
15 #include "typedef.h"
16 #include "basic_op.h"
17 #include "oper_32b.h"
18 #include "count.h"
19 #include "sig_proc.h"
20
21 /* local function */
22
23 static void Get_lsp_pol (Word16 *lsp, Word32 *f);
24
25 void Lsp_Az (
26 Word16 lsp[], /* (i) : line spectral frequencies */
27 Word16 a[] /* (o) : predictor coefficients (order = 10) */
28 )
29 {
30 Word16 i, j;
31 Word32 f1[6], f2[6];
32 Word32 t0;
33
34 Get_lsp_pol (&lsp[0], f1);
35 Get_lsp_pol (&lsp[1], f2);
36
37 for (i = 5; i > 0; i--)
38 {
39 f1[i] = L_add (f1[i], f1[i - 1]); move32 (); /* f1[i] += f1[i-1]; */
40 f2[i] = L_sub (f2[i], f2[i - 1]); move32 (); /* f2[i] -= f2[i-1]; */
41 }
42
43 a[0] = 4096; move16 ();
44 for (i = 1, j = 10; i <= 5; i++, j--)
45 {
46 t0 = L_add (f1[i], f2[i]); /* f1[i] + f2[i] */
47 a[i] = extract_l (L_shr_r (t0, 13)); move16 ();
48 t0 = L_sub (f1[i], f2[i]); /* f1[i] - f2[i] */
49 a[j] = extract_l (L_shr_r (t0, 13)); move16 ();
50 }
51
52 return;
53 }
54
55 /*************************************************************************
56 *
57 * FUNCTION: Get_lsp_pol
58 *
59 * PURPOSE: Find the polynomial F1(z) or F2(z) from the LSPs.
60 * If the LSP vector is passed at address 0 F1(z) is computed
61 * and if it is passed at address 1 F2(z) is computed.
62 *
63 * DESCRIPTION:
64 * This is performed by expanding the product polynomials:
65 *
66 * F1(z) = product ( 1 - 2 lsp[i] z^-1 + z^-2 )
67 * i=0,2,4,6,8
68 * F2(z) = product ( 1 - 2 lsp[i] z^-1 + z^-2 )
69 * i=1,3,5,7,9
70 *
71 * where lsp[] is the LSP vector in the cosine domain.
72 *
73 * The expansion is performed using the following recursion:
74 *
75 * f[0] = 1
76 * b = -2.0 * lsp[0]
77 * f[1] = b
78 * for i=2 to 5 do
79 * b = -2.0 * lsp[2*i-2];
80 * f[i] = b*f[i-1] + 2.0*f[i-2];
81 * for j=i-1 down to 2 do
82 * f[j] = f[j] + b*f[j-1] + f[j-2];
83 * f[1] = f[1] + b;
84 *
85 *************************************************************************/
86
87 static void Get_lsp_pol (Word16 *lsp, Word32 *f)
88 {
89 Word16 i, j, hi, lo;
90 Word32 t0;
91
92 /* f[0] = 1.0; */
93 *f = L_mult (4096, 2048); move32 ();
94 f++; move32 ();
95 *f = L_msu ((Word32) 0, *lsp, 512); /* f[1] = -2.0 * lsp[0]; */
96 f++; move32 ();
97 lsp += 2; /* Advance lsp pointer */
98
99 for (i = 2; i <= 5; i++)
100 {
101 *f = f[-2]; move32 ();
102
103 for (j = 1; j < i; j++, f--)
104 {
105 L_Extract (f[-1], &hi, &lo);
106 t0 = Mpy_32_16 (hi, lo, *lsp); /* t0 = f[-1] * lsp */
107 t0 = L_shl (t0, 1);
108 *f = L_add (*f, f[-2]); move32 (); /* *f += f[-2] */
109 *f = L_sub (*f, t0);move32 (); /* *f -= t0 */
110 }
111 *f = L_msu (*f, *lsp, 512); move32 (); /* *f -= lsp<<9 */
112 f += i; /* Advance f pointer */
113 lsp += 2; /* Advance lsp pointer */
114 }
115
116 return;
117 }