2 * Copyright (C) 2004-2010 NXP Software
3 * Copyright (C) 2010 The Android Open Source Project
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
9 * http://www.apache.org/licenses/LICENSE-2.0
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.
18 /************************************************************************/
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)*/
25 /************************************************************************/
27 /*######################################################################################*/
29 /*######################################################################################*/
31 #include "ScalarArithmetic.h"
34 /****************************************************************************************
35 * Name : dB_to_Lin32()
36 * Input : Signed 16-bit integer
38 * (15->05) = integer part
39 * (04->01) = decimal part
40 * Output : Signed 32-bit integer
42 * (31->16) = integer part
43 * (15->01) = decimal part
44 * Returns : Lin value format 1.16.15
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
50 * Correction = (Remainder / 1.5029) - (Remainder^2 / 6)
52 * The two coefficients are scaled from 0x40000000 in 96 steps and calculated
55 * FIRST_COEF = 0x80000000 / (96 * 1.5029)
56 * SECOND_COEF = 0x80000000 / (96^2 * 6)
58 ****************************************************************************************/
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 */
67 LVM_INT32 dB_to_Lin32(LVM_INT16 db_fix)
75 * Check sign of the input
79 if (db_fix > -MAX_VALUE)
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));
93 if (db_fix < MAX_VALUE)
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));
102 Lin_val_32 = 0x7FFFFFFF;
107 return Lin_val_32; /* format 1.16.15 */