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 "defines.h" 20 #include "constants.h" 21 22 /*----------------------------------------------------------------* 23 * conversion from lsf to lsp coefficients 24 *---------------------------------------------------------------*/ 25 26 void WebRtcIlbcfix_Lsf2Lsp( 27 int16_t *lsf, /* (i) lsf in Q13 values between 0 and pi */ 28 int16_t *lsp, /* (o) lsp in Q15 values between -1 and 1 */ 29 int16_t m /* (i) number of coefficients */ 30 ) { 31 int16_t i, k; 32 int16_t diff; /* difference, which is used for the 33 linear approximation (Q8) */ 34 int16_t freq; /* normalized frequency in Q15 (0..1) */ 35 int32_t tmpW32; 36 37 for(i=0; i<m; i++) 38 { 39 freq = (int16_t)WEBRTC_SPL_MUL_16_16_RSFT(lsf[i], 20861, 15); 40 /* 20861: 1.0/(2.0*PI) in Q17 */ 41 /* 42 Upper 8 bits give the index k and 43 Lower 8 bits give the difference, which needs 44 to be approximated linearly 45 */ 46 k = WEBRTC_SPL_RSHIFT_W16(freq, 8); 47 diff = (freq&0x00ff); 48 49 /* Guard against getting outside table */ 50 51 if (k>63) { 52 k = 63; 53 } 54 55 /* Calculate linear approximation */ 56 tmpW32 = WEBRTC_SPL_MUL_16_16(WebRtcIlbcfix_kCosDerivative[k], diff); 57 lsp[i] = WebRtcIlbcfix_kCos[k]+(int16_t)(WEBRTC_SPL_RSHIFT_W32(tmpW32, 12)); 58 } 59 60 return; 61 } 62
