eas_pan.c revision a8c89077d78769bf4840fa91609edc51fe2fa02d 
1/*----------------------------------------------------------------------------
2 *
3 * File:
4 * eas_pan.c
5 *
6 * Contents and purpose:
7 * Calculates left and right gain multipliers based on a pan value from -63 to +63
8 *
9 * NOTES:
10 * The _CMX_PARSER and _MFI_PARSER preprocessor symbols determine
11 * whether the parser works for those particular file formats.
12 *
13 * Copyright Sonic Network Inc. 2005
14
15 * Licensed under the Apache License, Version 2.0 (the "License");
16 * you may not use this file except in compliance with the License.
17 * You may obtain a copy of the License at
18 *
19 *      http://www.apache.org/licenses/LICENSE-2.0
20 *
21 * Unless required by applicable law or agreed to in writing, software
22 * distributed under the License is distributed on an "AS IS" BASIS,
23 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
24 * See the License for the specific language governing permissions and
25 * limitations under the License.
26 *
27 *----------------------------------------------------------------------------
28 * Revision Control:
29 *   $Revision: 82 $
30 *   $Date: 2006-07-10 11:45:19 -0700 (Mon, 10 Jul 2006) $
31 *----------------------------------------------------------------------------
32*/
33
34#include "eas_pan.h"
35#include "eas_math.h"
36
37/*----------------------------------------------------------------------------
38 * EAS_CalcPanControl()
39 *----------------------------------------------------------------------------
40 * Purpose:
41 * Assign the left and right gain values corresponding to the given pan value.
42 *
43 * This routine uses sin/cos approximations for an equal power curve:
44 *
45 * sin(x) = (2-4*c)*x^2 + c + x
46 * cos(x) = (2-4*c)*x^2 + c - x
47 *
48 * where  c = 1/sqrt(2)
49 * using the a0 + x*(a1 + x*a2) approach
50 *
51 * Inputs:
52 * pan          - pan value (-63 to + 63)
53 *
54 * Outputs:
55 * pGainLeft    linear gain multiplier for left channel (15-bit fraction)
56 * pGainRight   linear gain multiplier for left channel (15-bit fraction)
57 *
58 * Side Effects:
59 *----------------------------------------------------------------------------
60*/
61void EAS_CalcPanControl (EAS_INT pan, EAS_I16 *pGainLeft, EAS_I16 *pGainRight)
62{
63    EAS_INT temp;
64    EAS_INT netAngle;
65
66    /* impose hard limit */
67    if (pan < -63)
68        netAngle = -63;
69    else if (pan > 63)
70        netAngle = 63;
71    else
72        netAngle = pan;
73
74    /*lint -e{701} <avoid multiply for performance reasons>*/
75    netAngle = netAngle << 8;
76
77    /* calculate sin */
78    temp = EG1_ONE + FMUL_15x15(COEFF_PAN_G2, netAngle);
79    temp = COEFF_PAN_G0 + FMUL_15x15(temp, netAngle);
80
81    if (temp > SYNTH_FULL_SCALE_EG1_GAIN)
82        temp = SYNTH_FULL_SCALE_EG1_GAIN;
83    else if (temp < 0)
84        temp = 0;
85
86    *pGainRight = (EAS_I16) temp;
87
88    /* calculate cos */
89    temp = -EG1_ONE + FMUL_15x15(COEFF_PAN_G2, netAngle);
90    temp = COEFF_PAN_G0 + FMUL_15x15(temp, netAngle);
91    if (temp > SYNTH_FULL_SCALE_EG1_GAIN)
92        temp = SYNTH_FULL_SCALE_EG1_GAIN;
93    else if (temp < 0)
94        temp = 0;
95
96    *pGainLeft = (EAS_I16) temp;
97}
98
99