lpc_to_refl_coef.c (1712B)
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 * This file contains the function WebRtcSpl_LpcToReflCoef(). 13 * The description header can be found in signal_processing_library.h 14 * 15 */ 16 17 #include "common_audio/signal_processing/include/signal_processing_library.h" 18 19 #define SPL_LPC_TO_REFL_COEF_MAX_AR_MODEL_ORDER 50 20 21 void WebRtcSpl_LpcToReflCoef(int16_t* a16, int use_order, int16_t* k16) { 22 int m, k; 23 int32_t tmp32[SPL_LPC_TO_REFL_COEF_MAX_AR_MODEL_ORDER]; 24 int32_t tmp_inv_denom32; 25 int16_t tmp_inv_denom16; 26 27 k16[use_order - 1] = a16[use_order] << 3; // Q12<<3 => Q15 28 for (m = use_order - 1; m > 0; m--) { 29 // (1 - k^2) in Q30 30 tmp_inv_denom32 = 1073741823 - k16[m] * k16[m]; 31 // (1 - k^2) in Q15 32 tmp_inv_denom16 = (int16_t)(tmp_inv_denom32 >> 15); 33 34 for (k = 1; k <= m; k++) { 35 // tmp[k] = (a[k] - RC[m] * a[m-k+1]) / (1.0 - RC[m]*RC[m]); 36 37 // [Q12<<16 - (Q15*Q12)<<1] = [Q28 - Q28] = Q28 38 tmp32[k] = (a16[k] << 16) - (k16[m] * a16[m - k + 1] << 1); 39 40 tmp32[k] = 41 WebRtcSpl_DivW32W16(tmp32[k], tmp_inv_denom16); // Q28/Q15 = Q13 42 } 43 44 for (k = 1; k < m; k++) { 45 a16[k] = (int16_t)(tmp32[k] >> 1); // Q13>>1 => Q12 46 } 47 48 tmp32[m] = WEBRTC_SPL_SAT(8191, tmp32[m], -8191); 49 k16[m - 1] = (int16_t)WEBRTC_SPL_LSHIFT_W32(tmp32[m], 2); // Q13<<2 => Q15 50 } 51 return; 52 }