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/*
* Copyright (C) 2004-2010 NXP Software
* Copyright (C) 2010 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/************************************************************************/
/* */
/* %created_by: sra % (CM/S)*/
/* %name: dB_to_Lin32.c % (CM/S)*/
/* %version: 2 % (CM/S)*/
/* %date_created: Wed Jun 18 11:27:46 2008 % (CM/S)*/
/* */
/************************************************************************/
/*######################################################################################*/
/* Include files */
/*######################################################################################*/
#include "ScalarArithmetic.h"
/****************************************************************************************
* Name : dB_to_Lin32()
* Input : Signed 16-bit integer
* MSB (16) = sign bit
* (15->05) = integer part
* (04->01) = decimal part
* Output : Signed 32-bit integer
* MSB (32) = sign bit
* (31->16) = integer part
* (15->01) = decimal part
* Returns : Lin value format 1.16.15
* Description :
* Remarks : Makes an approximation to the conversion by counting the number
* of 6dB steps for use as shifts and then interpolates with a remainder
* with the equation:
*
* Correction = (Remainder / 1.5029) - (Remainder^2 / 6)
*
* The two coefficients are scaled from 0x40000000 in 96 steps and calculated
* as follows:
*
* FIRST_COEF = 0x80000000 / (96 * 1.5029)
* SECOND_COEF = 0x80000000 / (96^2 * 6)
*
****************************************************************************************/
#define FOUR_OVER_SIX 21846 /* (4 / 6) * 2^15 */
#define SIX_DB 96 /* 6 * 16 or 6dB in Q11.4 format */
#define FIRST_COEF_NEG 14884305
#define FIRST_COEF_POS 7442152 /* FIRST_COEF_NEG / 2 */
#define SECOND_COEF 38836
#define MAX_VALUE 1536 /* 96 * 16 */
LVM_INT32 dB_to_Lin32(LVM_INT16 db_fix)
{
LVM_INT32 Lin_val_32;
LVM_INT16 Shift;
LVM_INT32 Remain;
/*
* Check sign of the input
*/
if (db_fix<0)
{
if (db_fix > -MAX_VALUE)
{
Shift = (LVM_INT16)((((LVM_UINT32)(-db_fix) >> 4) * FOUR_OVER_SIX) >> 17); /* Number of 6dB steps in Q11.4 format */
Remain = -db_fix - (Shift * SIX_DB);
Remain = (0x7FFFFFFF - (Remain * FIRST_COEF_NEG)) + (Remain * Remain * SECOND_COEF);
Lin_val_32 = (LVM_INT32)((LVM_UINT32)Remain >> (16 + Shift));
}
else
{
Lin_val_32 = 0;
}
}
else
{
if (db_fix < MAX_VALUE)
{
Shift = (LVM_INT16)((((LVM_UINT32)db_fix >> 4) * FOUR_OVER_SIX) >> 17); /* Number of 6dB steps in Q11.4 format */
Remain = db_fix - (Shift * SIX_DB);
Remain = 0x3FFFFFFF + (Remain * FIRST_COEF_POS) + (Remain * Remain * SECOND_COEF);
Lin_val_32 = (LVM_INT32)((LVM_UINT32)Remain >> (15 - Shift));
}
else
{
Lin_val_32 = 0x7FFFFFFF;
}
}
return Lin_val_32; /* format 1.16.15 */
}
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