| /* |
| * Copyright (c) 2011 The WebRTC project authors. All Rights Reserved. |
| * |
| * Use of this source code is governed by a BSD-style license |
| * that can be found in the LICENSE file in the root of the source |
| * tree. An additional intellectual property rights grant can be found |
| * in the file PATENTS. All contributing project authors may |
| * be found in the AUTHORS file in the root of the source tree. |
| */ |
| |
| /****************************************************************** |
| |
| iLBC Speech Coder ANSI-C Source Code |
| |
| WebRtcIlbcfix_Lsf2Lsp.c |
| |
| ******************************************************************/ |
| |
| #include "defines.h" |
| #include "constants.h" |
| |
| /*----------------------------------------------------------------* |
| * conversion from lsf to lsp coefficients |
| *---------------------------------------------------------------*/ |
| |
| void WebRtcIlbcfix_Lsf2Lsp( |
| WebRtc_Word16 *lsf, /* (i) lsf in Q13 values between 0 and pi */ |
| WebRtc_Word16 *lsp, /* (o) lsp in Q15 values between -1 and 1 */ |
| WebRtc_Word16 m /* (i) number of coefficients */ |
| ) { |
| WebRtc_Word16 i, k; |
| WebRtc_Word16 diff; /* difference, which is used for the |
| linear approximation (Q8) */ |
| WebRtc_Word16 freq; /* normalized frequency in Q15 (0..1) */ |
| WebRtc_Word32 tmpW32; |
| |
| for(i=0; i<m; i++) |
| { |
| freq = (WebRtc_Word16)WEBRTC_SPL_MUL_16_16_RSFT(lsf[i], 20861, 15); |
| /* 20861: 1.0/(2.0*PI) in Q17 */ |
| /* |
| Upper 8 bits give the index k and |
| Lower 8 bits give the difference, which needs |
| to be approximated linearly |
| */ |
| k = WEBRTC_SPL_RSHIFT_W16(freq, 8); |
| diff = (freq&0x00ff); |
| |
| /* Guard against getting outside table */ |
| |
| if (k>63) { |
| k = 63; |
| } |
| |
| /* Calculate linear approximation */ |
| tmpW32 = WEBRTC_SPL_MUL_16_16(WebRtcIlbcfix_kCosDerivative[k], diff); |
| lsp[i] = WebRtcIlbcfix_kCos[k]+(WebRtc_Word16)(WEBRTC_SPL_RSHIFT_W32(tmpW32, 12)); |
| } |
| |
| return; |
| } |