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_LpcToReflCoef(). 14 * The description header can be found in signal_processing_library.h 15 * 16 */ 17 18 #include "signal_processing_library.h" 19 20 #define SPL_LPC_TO_REFL_COEF_MAX_AR_MODEL_ORDER 50 21 22 void WebRtcSpl_LpcToReflCoef(WebRtc_Word16* a16, int use_order, WebRtc_Word16* k16) 23 { 24 int m, k; 25 WebRtc_Word32 tmp32[SPL_LPC_TO_REFL_COEF_MAX_AR_MODEL_ORDER]; 26 WebRtc_Word32 tmp_inv_denom32; 27 WebRtc_Word16 tmp_inv_denom16; 28 29 k16[use_order - 1] = WEBRTC_SPL_LSHIFT_W16(a16[use_order], 3); //Q12<<3 => Q15 30 for (m = use_order - 1; m > 0; m--) 31 { 32 // (1 - k^2) in Q30 33 tmp_inv_denom32 = ((WebRtc_Word32)1073741823) - WEBRTC_SPL_MUL_16_16(k16[m], k16[m]); 34 // (1 - k^2) in Q15 35 tmp_inv_denom16 = (WebRtc_Word16)WEBRTC_SPL_RSHIFT_W32(tmp_inv_denom32, 15); 36 37 for (k = 1; k <= m; k++) 38 { 39 // tmp[k] = (a[k] - RC[m] * a[m-k+1]) / (1.0 - RC[m]*RC[m]); 40 41 // [Q12<<16 - (Q15*Q12)<<1] = [Q28 - Q28] = Q28 42 tmp32[k] = WEBRTC_SPL_LSHIFT_W32((WebRtc_Word32)a16[k], 16) 43 - WEBRTC_SPL_LSHIFT_W32(WEBRTC_SPL_MUL_16_16(k16[m], a16[m-k+1]), 1); 44 45 tmp32[k] = WebRtcSpl_DivW32W16(tmp32[k], tmp_inv_denom16); //Q28/Q15 = Q13 46 } 47 48 for (k = 1; k < m; k++) 49 { 50 a16[k] = (WebRtc_Word16)WEBRTC_SPL_RSHIFT_W32(tmp32[k], 1); //Q13>>1 => Q12 51 } 52 53 tmp32[m] = WEBRTC_SPL_SAT(8191, tmp32[m], -8191); 54 k16[m - 1] = (WebRtc_Word16)WEBRTC_SPL_LSHIFT_W32(tmp32[m], 2); //Q13<<2 => Q15 55 } 56 return; 57 } 58
