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 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)) = (int16_t)(WEBRTC_SPL_RSHIFT_W32(((int32_t)(*a_i_ptr)+(*a_10mi_ptr)), 2) - (*f1ptr)); 60 (*(f2ptr+1)) = (int16_t)(WEBRTC_SPL_RSHIFT_W32(((int32_t)(*a_i_ptr)-(*a_10mi_ptr)), 2) + (*f2ptr)); 61 a_i_ptr++; 62 a_10mi_ptr--; 63 f1ptr++; 64 f2ptr++; 65 } 66 67 /* 68 find the LSPs using the Chebychev pol. evaluation 69 */ 70 71 fi_select = 0; /* selector between f1 and f2, start with f1 */ 72 73 foundFreqs = 0; 74 75 xlow = WebRtcIlbcfix_kCosGrid[0]; 76 ylow = WebRtcIlbcfix_Chebyshev(xlow, f[fi_select]); 77 78 /* 79 Iterate until all the 10 LSP's have been found or 80 all the grid points have been tried. If the 10 LSP's can 81 not be found, set the LSP vector to previous LSP 82 */ 83 84 for (j = 1; j < COS_GRID_POINTS && foundFreqs < 10; j++) { 85 xhigh = xlow; 86 yhigh = ylow; 87 xlow = WebRtcIlbcfix_kCosGrid[j]; 88 ylow = WebRtcIlbcfix_Chebyshev(xlow, f[fi_select]); 89 90 if (WEBRTC_SPL_MUL_16_16(ylow, yhigh) <= 0) { 91 /* Run 4 times to reduce the interval */ 92 for (i = 0; i < 4; i++) { 93 /* xmid =(xlow + xhigh)/2 */ 94 xmid = WEBRTC_SPL_RSHIFT_W16(xlow, 1) + WEBRTC_SPL_RSHIFT_W16(xhigh, 1); 95 ymid = WebRtcIlbcfix_Chebyshev(xmid, f[fi_select]); 96 97 if (WEBRTC_SPL_MUL_16_16(ylow, ymid) <= 0) { 98 yhigh = ymid; 99 xhigh = xmid; 100 } else { 101 ylow = ymid; 102 xlow = xmid; 103 } 104 } 105 106 /* 107 Calculater xint by linear interpolation: 108 xint = xlow - ylow*(xhigh-xlow)/(yhigh-ylow); 109 */ 110 111 x = xhigh - xlow; 112 y = yhigh - ylow; 113 114 if (y == 0) { 115 xint = xlow; 116 } else { 117 sign = y; 118 y = WEBRTC_SPL_ABS_W16(y); 119 shifts = (int16_t)WebRtcSpl_NormW32(y)-16; 120 y = WEBRTC_SPL_LSHIFT_W16(y, shifts); 121 y = (int16_t)WebRtcSpl_DivW32W16(536838144, y); /* 1/(yhigh-ylow) */ 122 123 tmpW32 = WEBRTC_SPL_MUL_16_16_RSFT(x, y, (19-shifts)); 124 125 /* y=(xhigh-xlow)/(yhigh-ylow) */ 126 y = (int16_t)(tmpW32&0xFFFF); 127 128 if (sign < 0) { 129 y = -y; 130 } 131 /* tmpW32 = ylow*(xhigh-xlow)/(yhigh-ylow) */ 132 tmpW32 = WEBRTC_SPL_MUL_16_16_RSFT(ylow, y, 10); 133 xint = xlow-(int16_t)(tmpW32&0xFFFF); 134 } 135 136 /* Store the calculated lsp */ 137 lsp[foundFreqs] = (int16_t)xint; 138 foundFreqs++; 139 140 /* if needed, set xlow and ylow for next recursion */ 141 if (foundFreqs<10) { 142 xlow = xint; 143 /* Swap between f1 and f2 (f[0][] and f[1][]) */ 144 fi_select = ((fi_select+1)&0x1); 145 146 ylow = WebRtcIlbcfix_Chebyshev(xlow, f[fi_select]); 147 } 148 } 149 } 150 151 /* Check if M roots found, if not then use the old LSP */ 152 if (foundFreqs < 10) { 153 WEBRTC_SPL_MEMCPY_W16(lsp, old_lsp, 10); 154 } 155 return; 156 } 157
