| /* |
| * 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 */ |
| } |
| |
