xref: /frameworks/av/media/libeffects/lvm/lib/Common/src/dB_to_Lin32.c

/*
 * 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 */
}