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
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
67LVM_INT32   dB_to_Lin32(LVM_INT16    db_fix)
68{
69    LVM_INT32 Lin_val_32;
70    LVM_INT16 Shift;
71    LVM_INT32 Remain;
72
73
74    /*
75     * Check sign of the input
76     */
77    if (db_fix<0)
78    {
79        if (db_fix > -MAX_VALUE)
80        {
81            Shift  = (LVM_INT16)((((LVM_UINT32)(-db_fix) >> 4) * FOUR_OVER_SIX) >> 17);        /* Number of 6dB steps in Q11.4 format */
82            Remain = -db_fix - (Shift * SIX_DB);
83            Remain = (0x7FFFFFFF - (Remain * FIRST_COEF_NEG)) + (Remain * Remain * SECOND_COEF);
84            Lin_val_32 = (LVM_INT32)((LVM_UINT32)Remain >> (16 + Shift));
85        }
86        else
87        {
88            Lin_val_32 = 0;
89        }
90    }
91    else
92    {
93        if (db_fix < MAX_VALUE)
94        {
95            Shift  = (LVM_INT16)((((LVM_UINT32)db_fix >> 4) * FOUR_OVER_SIX) >> 17);        /* Number of 6dB steps in Q11.4 format */
96            Remain = db_fix - (Shift * SIX_DB);
97            Remain = 0x3FFFFFFF + (Remain * FIRST_COEF_POS) + (Remain * Remain * SECOND_COEF);
98            Lin_val_32 = (LVM_INT32)((LVM_UINT32)Remain >> (15 - Shift));
99        }
100        else
101        {
102            Lin_val_32 = 0x7FFFFFFF;
103        }
104    }
105
106
107    return Lin_val_32;  /* format 1.16.15 */
108}
109
110