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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  * This file contains the function WebRtcSpl_AutoCorrToReflCoef().
     14  * The description header can be found in signal_processing_library.h
     15  *
     16  */
     17 
     18 #include "signal_processing_library.h"
     19 
     20 void WebRtcSpl_AutoCorrToReflCoef(G_CONST WebRtc_Word32 *R, int use_order, WebRtc_Word16 *K)
     21 {
     22     int i, n;
     23     WebRtc_Word16 tmp;
     24     G_CONST WebRtc_Word32 *rptr;
     25     WebRtc_Word32 L_num, L_den;
     26     WebRtc_Word16 *acfptr, *pptr, *wptr, *p1ptr, *w1ptr, ACF[WEBRTC_SPL_MAX_LPC_ORDER],
     27             P[WEBRTC_SPL_MAX_LPC_ORDER], W[WEBRTC_SPL_MAX_LPC_ORDER];
     28 
     29     // Initialize loop and pointers.
     30     acfptr = ACF;
     31     rptr = R;
     32     pptr = P;
     33     p1ptr = &P[1];
     34     w1ptr = &W[1];
     35     wptr = w1ptr;
     36 
     37     // First loop; n=0. Determine shifting.
     38     tmp = WebRtcSpl_NormW32(*R);
     39     *acfptr = (WebRtc_Word16)((*rptr++ << tmp) >> 16);
     40     *pptr++ = *acfptr++;
     41 
     42     // Initialize ACF, P and W.
     43     for (i = 1; i <= use_order; i++)
     44     {
     45         *acfptr = (WebRtc_Word16)((*rptr++ << tmp) >> 16);
     46         *wptr++ = *acfptr;
     47         *pptr++ = *acfptr++;
     48     }
     49 
     50     // Compute reflection coefficients.
     51     for (n = 1; n <= use_order; n++, K++)
     52     {
     53         tmp = WEBRTC_SPL_ABS_W16(*p1ptr);
     54         if (*P < tmp)
     55         {
     56             for (i = n; i <= use_order; i++)
     57                 *K++ = 0;
     58 
     59             return;
     60         }
     61 
     62         // Division: WebRtcSpl_div(tmp, *P)
     63         *K = 0;
     64         if (tmp != 0)
     65         {
     66             L_num = tmp;
     67             L_den = *P;
     68             i = 15;
     69             while (i--)
     70             {
     71                 (*K) <<= 1;
     72                 L_num <<= 1;
     73                 if (L_num >= L_den)
     74                 {
     75                     L_num -= L_den;
     76                     (*K)++;
     77                 }
     78             }
     79             if (*p1ptr > 0)
     80                 *K = -*K;
     81         }
     82 
     83         // Last iteration; don't do Schur recursion.
     84         if (n == use_order)
     85             return;
     86 
     87         // Schur recursion.
     88         pptr = P;
     89         wptr = w1ptr;
     90         tmp = (WebRtc_Word16)(((WebRtc_Word32)*p1ptr * (WebRtc_Word32)*K + 16384) >> 15);
     91         *pptr = WEBRTC_SPL_ADD_SAT_W16( *pptr, tmp );
     92         pptr++;
     93         for (i = 1; i <= use_order - n; i++)
     94         {
     95             tmp = (WebRtc_Word16)(((WebRtc_Word32)*wptr * (WebRtc_Word32)*K + 16384) >> 15);
     96             *pptr = WEBRTC_SPL_ADD_SAT_W16( *(pptr+1), tmp );
     97             pptr++;
     98             tmp = (WebRtc_Word16)(((WebRtc_Word32)*pptr * (WebRtc_Word32)*K + 16384) >> 15);
     99             *wptr = WEBRTC_SPL_ADD_SAT_W16( *wptr, tmp );
    100             wptr++;
    101         }
    102     }
    103 }
    104