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/*    Includes                                                                          */
21/*                                                                                      */
22/****************************************************************************************/
23
24#include "CompLim_private.h"
25
26/****************************************************************************************/
27/*                                                                                      */
28/* FUNCTION:                 NonLinComp_D16                                             */
29/*                                                                                      */
30/* DESCRIPTION:                                                                         */
31/*  Non-linear compression by companding. The function works on a sample by sample      */
32/*  basis by increasing the level near the zero crossing. This gives a ttrade-off       */
33/*  between THD and compression. It uses the equation:                                  */
34/*                                                                                      */
35/*        Output = Input + K * (Input - Input^2)        if Input >  0                   */
36/*               = Input + K * (Input + Input^2)      if Input <= 0                     */
37/*                                                                                      */
38/*    The value of K controls the amount of compression and as a side effect the amount */
39/*  distortion introduced. The amount of compression is signal dependent and the values */
40/*  given below are approximate.                                                        */
41/*                                                                                      */
42/*        Gain (fractional)  Gain (integer)    Compression          Pk-Pk THD           */
43/*            1.0                 32767            +6dB            16dB                 */
44/*            0.78                25559            +5dB            19dB                 */
45/*            0.6                 19661            +4dB            21dB                 */
46/*            0.41                13435            +3dB            24dB                 */
47/*            0.26                 8520            +2dB            28dB                 */
48/*            0.12                 3932            +1dB            34dB                 */
49/*            0.0                     0            +0dB            98dB                 */
50/*                                                                                      */
51/* PARAMETERS:                                                                          */
52/*    Gain            -    compression control parameter                                */
53/*    pDataIn         -    pointer to the input data buffer                             */
54/*    pDataOut        -    pointer to the output data buffer                            */
55/*    BlockLength     -    number of samples to process                                 */
56/*                                                                                      */
57/* RETURNS:                                                                             */
58/*    None                                                                              */
59/*                                                                                      */
60/* NOTES:                                                                               */
61/*                                                                                      */
62/****************************************************************************************/
63
64void NonLinComp_D16(LVM_INT16        Gain,
65                      LVM_INT16        *pDataIn,
66                    LVM_INT16        *pDataOut,
67                    LVM_INT32        BlockLength)
68{
69
70    LVM_INT16            Sample;                    /* Input samples */
71    LVM_INT32            SampleNo;                /* Sample index */
72    LVM_INT16            Temp;
73
74
75    /*
76     * Process a block of samples
77     */
78    for(SampleNo = 0; SampleNo<BlockLength; SampleNo++)
79    {
80
81        /*
82         * Read the input
83         */
84        Sample = *pDataIn;
85        pDataIn++;
86
87
88        /*
89         * Apply the compander, this compresses the signal at the expense of
90         * harmonic distortion. The amount of compression is control by the
91         * gain factor
92         */
93        if ((LVM_INT32)Sample != -32768)
94        {
95            Temp = (LVM_INT16)((Sample * Sample) >> 15);
96            if(Sample >0)
97            {
98                Sample = (LVM_INT16)(Sample + ((Gain * (Sample - Temp)) >> 15));
99            }
100            else
101            {
102                Sample = (LVM_INT16)(Sample + ((Gain * (Sample + Temp)) >> 15));
103            }
104        }
105
106
107        /*
108         * Save the output
109         */
110        *pDataOut = Sample;
111        pDataOut++;
112
113
114    }
115
116}
117
118