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#include "LVM_Types.h"
19#include "LVM_Macros.h"
20#include "Mixer.h"
21#include "LVM_Mixer_FilterCoeffs.h"
22
23
24/************************************************************************/
25/* FUNCTION:                                                            */
26/*   LVM_Mix_GetTimeConstant                                            */
27/*                                                                      */
28/* DESCRIPTION:                                                         */
29/*  This function calculates the filter coefficient using the following */
30/*  equation:                                                           */
31/*       Alpha = exp(ln(0.1)/ (tc * Update + 1.0))                      */
32/*                                                                      */
33/*  This is to be used with the follow first order filter, called at a  */
34/*  rate of Update times a second. tc is the required time constant in  */
35/*  units of 100us.                                                     */
36/*                                                                      */
37/*       Output(n) = Alpha * Output(n-1) + (1 - Alpha) * Target(n)      */
38/*                                                                      */
39/*  The function assumes the block size is large, i.e. the update rate  */
40/*  is approximately a fixed, and correct factor of the value of Fs     */
41/*  given in the call. This is especially not true when the block size  */
42/*  is very small, see the mixer documentation for further details.     */
43/*                                                                      */
44/*  The function does not support all possible combinations of input    */
45/*  values:                                                             */
46/*                                                                      */
47/*  1. NumChannels is limited to the values 1 (Mono) and 2 (Stereo)     */
48/*  2. The product tc * Fs is limited approximately to the range        */
49/*      8 < (tc * Fs) < 2^35                                            */
50/*                                                                      */
51/* PARAMETERS:                                                          */
52/*  tc              - the time constant in 100us steps, i.e. 10 = 1ms   */
53/*  Fs              - the filter update rate in Hz                      */
54/*  NumChannels     - Number of channels 1=Mono, 2=Stereo               */
55/*                                                                      */
56/* RETURNS:                                                             */
57/*  Alpha   - the filter coefficient Q31 format                         */
58/*                                                                      */
59/************************************************************************/
60
61LVM_UINT32 LVM_Mixer_TimeConstant(LVM_UINT32   tc,
62                                  LVM_UINT16   Fs,
63                                  LVM_UINT16   NumChannels)
64{
65
66    LVM_UINT32  Product;
67    LVM_INT16   Interpolate;
68    LVM_UINT16  Shift;
69    LVM_INT32   Diff;
70    LVM_UINT32  Table[] = {ALPHA_0,             /* Log spaced look-up table */
71                           ALPHA_1,
72                           ALPHA_2,
73                           ALPHA_3,
74                           ALPHA_4,
75                           ALPHA_5,
76                           ALPHA_6,
77                           ALPHA_7,
78                           ALPHA_8,
79                           ALPHA_9,
80                           ALPHA_10,
81                           ALPHA_11,
82                           ALPHA_12,
83                           ALPHA_13,
84                           ALPHA_14,
85                           ALPHA_15,
86                           ALPHA_16,
87                           ALPHA_17,
88                           ALPHA_18,
89                           ALPHA_19,
90                           ALPHA_20,
91                           ALPHA_21,
92                           ALPHA_22,
93                           ALPHA_23,
94                           ALPHA_24,
95                           ALPHA_25,
96                           ALPHA_26,
97                           ALPHA_27,
98                           ALPHA_28,
99                           ALPHA_29,
100                           ALPHA_30,
101                           ALPHA_31,
102                           ALPHA_32,
103                           ALPHA_33,
104                           ALPHA_34,
105                           ALPHA_35,
106                           ALPHA_36,
107                           ALPHA_37,
108                           ALPHA_38,
109                           ALPHA_39,
110                           ALPHA_40,
111                           ALPHA_41,
112                           ALPHA_42,
113                           ALPHA_43,
114                           ALPHA_44,
115                           ALPHA_45,
116                           ALPHA_46,
117                           ALPHA_47,
118                           ALPHA_48,
119                           ALPHA_49,
120                           ALPHA_50};
121
122
123    /* Calculate the product of the time constant and the sample rate */
124    Product = ((tc >> 16) * (LVM_UINT32)Fs) << 13;  /* Stereo value */
125    Product = Product + (((tc & 0x0000FFFF) * (LVM_UINT32)Fs) >> 3);
126
127    if (NumChannels == 1)
128    {
129        Product = Product >> 1;   /* Mono value */
130    }
131
132    /* Normalize to get the table index and interpolation factor */
133    for (Shift=0; Shift<((Alpha_TableSize-1)/2); Shift++)
134    {
135        if ((Product & 0x80000000)!=0)
136        {
137            break;
138        }
139
140        Product = Product << 1;
141    }
142    Shift = (LVM_UINT16)((Shift << 1));
143
144    if ((Product & 0x40000000)==0)
145    {
146        Shift++;
147    }
148
149    Interpolate = (LVM_INT16)((Product >> 15) & 0x00007FFF);
150
151    Diff = (LVM_INT32)(Table[Shift] - Table[Shift+1]);
152    MUL32x16INTO32(Diff,Interpolate,Diff,15)
153        Product = Table[Shift+1] + (LVM_UINT32)Diff;
154
155    return Product;
156}
157