1 /*
2 * Copyright (C) 2004-2010 NXP Software
3 * Copyright (C) 2010 The Android Open Source Project
4 *
5 * Licensed under the Apache License, Version 2.0 (the "License");
6 * you may not use this file except in compliance with the License.
7 * You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17
18 /************************************************************************/
19 /* */
20 /* %created_by: sra % (CM/S)*/
21 /* %name: dB_to_Lin32.c % (CM/S)*/
22 /* %version: 2 % (CM/S)*/
23 /* %date_created: Wed Jun 18 11:27:46 2008 % (CM/S)*/
24 /* */
25 /************************************************************************/
26
27 /*######################################################################################*/
28 /* Include files */
29 /*######################################################################################*/
30
31 #include "ScalarArithmetic.h"
32 #include <math.h>
33
34 /****************************************************************************************
35 * Name : dB_to_Lin32()
36 * Input : Signed 16-bit integer
37 * MSB (16) = sign bit
38 * (15->05) = integer part
39 * (04->01) = decimal part
40 * Output : Signed 32-bit integer
41 * MSB (32) = sign bit
42 * (31->16) = integer part
43 * (15->01) = decimal part
44 * Returns : Lin value format 1.16.15
45 * Description :
46 * Remarks : Makes an approximation to the conversion by counting the number
47 * of 6dB steps for use as shifts and then interpolates with a remainder
48 * with the equation:
49 *
50 * Correction = (Remainder / 1.5029) - (Remainder^2 / 6)
51 *
52 * The two coefficients are scaled from 0x40000000 in 96 steps and calculated
53 * as follows:
54 *
55 * FIRST_COEF = 0x80000000 / (96 * 1.5029)
56 * SECOND_COEF = 0x80000000 / (96^2 * 6)
57 *
58 ****************************************************************************************/
59
60 #define FOUR_OVER_SIX 21846 /* (4 / 6) * 2^15 */
61 #define SIX_DB 96 /* 6 * 16 or 6dB in Q11.4 format */
62 #define FIRST_COEF_NEG 14884305
63 #define FIRST_COEF_POS 7442152 /* FIRST_COEF_NEG / 2 */
64 #define SECOND_COEF 38836
65 #define MAX_VALUE 1536 /* 96 * 16 */
66
dB_to_LinFloat(LVM_INT16 db_fix)67 LVM_FLOAT dB_to_LinFloat(LVM_INT16 db_fix)
68 {
69 LVM_FLOAT dB_Float;
70 LVM_FLOAT LinFloat;
71
72 dB_Float = (LVM_FLOAT)((LVM_FLOAT)db_fix / 16.0f);
73 LinFloat = pow(10, dB_Float / 20.0);
74
75 return LinFloat;
76 }
77