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_Lsf2Lsp.c 16 17 ******************************************************************/ 18 19 #include "modules/audio_coding/codecs/ilbc/lsf_to_lsp.h" 20 21 #include "modules/audio_coding/codecs/ilbc/constants.h" 22 #include "modules/audio_coding/codecs/ilbc/defines.h" 23 24 /*----------------------------------------------------------------* 25 * conversion from lsf to lsp coefficients 26 *---------------------------------------------------------------*/ 27 WebRtcIlbcfix_Lsf2Lsp(int16_t * lsf,int16_t * lsp,int16_t m)28void WebRtcIlbcfix_Lsf2Lsp( 29 int16_t *lsf, /* (i) lsf in Q13 values between 0 and pi */ 30 int16_t *lsp, /* (o) lsp in Q15 values between -1 and 1 */ 31 int16_t m /* (i) number of coefficients */ 32 ) { 33 int16_t i, k; 34 int16_t diff; /* difference, which is used for the 35 linear approximation (Q8) */ 36 int16_t freq; /* normalized frequency in Q15 (0..1) */ 37 int32_t tmpW32; 38 39 for(i=0; i<m; i++) 40 { 41 freq = (int16_t)((lsf[i] * 20861) >> 15); 42 /* 20861: 1.0/(2.0*PI) in Q17 */ 43 /* 44 Upper 8 bits give the index k and 45 Lower 8 bits give the difference, which needs 46 to be approximated linearly 47 */ 48 k = freq >> 8; 49 diff = (freq&0x00ff); 50 51 /* Guard against getting outside table */ 52 53 if (k>63) { 54 k = 63; 55 } 56 57 /* Calculate linear approximation */ 58 tmpW32 = WebRtcIlbcfix_kCosDerivative[k] * diff; 59 lsp[i] = WebRtcIlbcfix_kCos[k] + (int16_t)(tmpW32 >> 12); 60 } 61 62 return; 63 } 64