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      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_GetLspPoly.c
     16 
     17 ******************************************************************/
     18 
     19 #include "defines.h"
     20 
     21 /*----------------------------------------------------------------*
     22  * Construct the polynomials F1(z) and F2(z) from the LSP
     23  * (Computations are done in Q24)
     24  *
     25  * The expansion is performed using the following recursion:
     26  *
     27  * f[0] = 1;
     28  * tmp = -2.0 * lsp[0];
     29  * f[1] = tmp;
     30  * for (i=2; i<=5; i++) {
     31  *    b = -2.0 * lsp[2*i-2];
     32  *    f[i] = tmp*f[i-1] + 2.0*f[i-2];
     33  *    for (j=i; j>=2; j--) {
     34  *       f[j] = f[j] + tmp*f[j-1] + f[j-2];
     35  *    }
     36  *    f[i] = f[i] + tmp;
     37  * }
     38  *---------------------------------------------------------------*/
     39 
     40 void WebRtcIlbcfix_GetLspPoly(
     41     int16_t *lsp, /* (i) LSP in Q15 */
     42     int32_t *f)  /* (o) polonymial in Q24 */
     43 {
     44   int32_t tmpW32;
     45   int i, j;
     46   int16_t high, low;
     47   int16_t *lspPtr;
     48   int32_t *fPtr;
     49 
     50   lspPtr = lsp;
     51   fPtr = f;
     52   /* f[0] = 1.0 (Q24) */
     53   (*fPtr) = (int32_t)16777216;
     54   fPtr++;
     55 
     56   (*fPtr) = WEBRTC_SPL_MUL((*lspPtr), -1024);
     57   fPtr++;
     58   lspPtr+=2;
     59 
     60   for(i=2; i<=5; i++)
     61   {
     62     (*fPtr) = fPtr[-2];
     63 
     64     for(j=i; j>1; j--)
     65     {
     66       /* Compute f[j] = f[j] + tmp*f[j-1] + f[j-2]; */
     67       high = (int16_t)(fPtr[-1] >> 16);
     68       low = (int16_t)((fPtr[-1] - ((int32_t)high << 16)) >> 1);
     69 
     70       tmpW32 = ((high * *lspPtr) << 2) + (((low * *lspPtr) >> 15) << 2);
     71 
     72       (*fPtr) += fPtr[-2];
     73       (*fPtr) -= tmpW32;
     74       fPtr--;
     75     }
     76     *fPtr -= *lspPtr << 10;
     77 
     78     fPtr+=i;
     79     lspPtr+=2;
     80   }
     81   return;
     82 }
     83