1 /*
2 * Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
3 *
4 * Use of this source code is governed by a BSD-style license
5 * that can be found in the LICENSE file in the root of the source
6 * tree. An additional intellectual property rights grant can be found
7 * in the file PATENTS. All contributing project authors may
8 * be found in the AUTHORS file in the root of the source tree.
9 */
10
11 /******************************************************************
12
13 iLBC Speech Coder ANSI-C Source Code
14
15 WebRtcIlbcfix_Poly2Lsp.c
16
17 ******************************************************************/
18
19 #include "defines.h"
20 #include "constants.h"
21 #include "chebyshev.h"
22
23 /*----------------------------------------------------------------*
24 * conversion from lpc coefficients to lsp coefficients
25 * function is only for 10:th order LPC
26 *---------------------------------------------------------------*/
27
WebRtcIlbcfix_Poly2Lsp(int16_t * a,int16_t * lsp,int16_t * old_lsp)28 void WebRtcIlbcfix_Poly2Lsp(
29 int16_t *a, /* (o) A coefficients in Q12 */
30 int16_t *lsp, /* (i) LSP coefficients in Q15 */
31 int16_t *old_lsp /* (i) old LSP coefficients that are used if the new
32 coefficients turn out to be unstable */
33 ) {
34 int16_t f[2][6]; /* f[0][] represents f1 and f[1][] represents f2 */
35 int16_t *a_i_ptr, *a_10mi_ptr;
36 int16_t *f1ptr, *f2ptr;
37 int32_t tmpW32;
38 int16_t x, y, xlow, ylow, xmid, ymid, xhigh, yhigh, xint;
39 int16_t shifts, sign;
40 int i, j;
41 int foundFreqs;
42 int fi_select;
43
44 /*
45 Calculate the two polynomials f1(z) and f2(z)
46 (the sum and the diff polynomial)
47 f1[0] = f2[0] = 1.0;
48 f1[i+1] = a[i+1] + a[10-i] - f1[i];
49 f2[i+1] = a[i+1] - a[10-i] - f1[i];
50 */
51
52 a_i_ptr = a + 1;
53 a_10mi_ptr = a + 10;
54 f1ptr = f[0];
55 f2ptr = f[1];
56 (*f1ptr) = 1024; /* 1.0 in Q10 */
57 (*f2ptr) = 1024; /* 1.0 in Q10 */
58 for (i = 0; i < 5; i++) {
59 *(f1ptr + 1) =
60 (int16_t)((((int32_t)(*a_i_ptr) + *a_10mi_ptr) >> 2) - *f1ptr);
61 *(f2ptr + 1) =
62 (int16_t)((((int32_t)(*a_i_ptr) - *a_10mi_ptr) >> 2) + *f2ptr);
63 a_i_ptr++;
64 a_10mi_ptr--;
65 f1ptr++;
66 f2ptr++;
67 }
68
69 /*
70 find the LSPs using the Chebychev pol. evaluation
71 */
72
73 fi_select = 0; /* selector between f1 and f2, start with f1 */
74
75 foundFreqs = 0;
76
77 xlow = WebRtcIlbcfix_kCosGrid[0];
78 ylow = WebRtcIlbcfix_Chebyshev(xlow, f[fi_select]);
79
80 /*
81 Iterate until all the 10 LSP's have been found or
82 all the grid points have been tried. If the 10 LSP's can
83 not be found, set the LSP vector to previous LSP
84 */
85
86 for (j = 1; j < COS_GRID_POINTS && foundFreqs < 10; j++) {
87 xhigh = xlow;
88 yhigh = ylow;
89 xlow = WebRtcIlbcfix_kCosGrid[j];
90 ylow = WebRtcIlbcfix_Chebyshev(xlow, f[fi_select]);
91
92 if (ylow * yhigh <= 0) {
93 /* Run 4 times to reduce the interval */
94 for (i = 0; i < 4; i++) {
95 /* xmid =(xlow + xhigh)/2 */
96 xmid = (xlow >> 1) + (xhigh >> 1);
97 ymid = WebRtcIlbcfix_Chebyshev(xmid, f[fi_select]);
98
99 if (ylow * ymid <= 0) {
100 yhigh = ymid;
101 xhigh = xmid;
102 } else {
103 ylow = ymid;
104 xlow = xmid;
105 }
106 }
107
108 /*
109 Calculater xint by linear interpolation:
110 xint = xlow - ylow*(xhigh-xlow)/(yhigh-ylow);
111 */
112
113 x = xhigh - xlow;
114 y = yhigh - ylow;
115
116 if (y == 0) {
117 xint = xlow;
118 } else {
119 sign = y;
120 y = WEBRTC_SPL_ABS_W16(y);
121 shifts = (int16_t)WebRtcSpl_NormW32(y)-16;
122 y <<= shifts;
123 y = (int16_t)WebRtcSpl_DivW32W16(536838144, y); /* 1/(yhigh-ylow) */
124
125 tmpW32 = (x * y) >> (19 - shifts);
126
127 /* y=(xhigh-xlow)/(yhigh-ylow) */
128 y = (int16_t)(tmpW32&0xFFFF);
129
130 if (sign < 0) {
131 y = -y;
132 }
133 /* tmpW32 = ylow*(xhigh-xlow)/(yhigh-ylow) */
134 tmpW32 = (ylow * y) >> 10;
135 xint = xlow-(int16_t)(tmpW32&0xFFFF);
136 }
137
138 /* Store the calculated lsp */
139 lsp[foundFreqs] = (int16_t)xint;
140 foundFreqs++;
141
142 /* if needed, set xlow and ylow for next recursion */
143 if (foundFreqs<10) {
144 xlow = xint;
145 /* Swap between f1 and f2 (f[0][] and f[1][]) */
146 fi_select = ((fi_select+1)&0x1);
147
148 ylow = WebRtcIlbcfix_Chebyshev(xlow, f[fi_select]);
149 }
150 }
151 }
152
153 /* Check if M roots found, if not then use the old LSP */
154 if (foundFreqs < 10) {
155 WEBRTC_SPL_MEMCPY_W16(lsp, old_lsp, 10);
156 }
157 return;
158 }
159