1 /* 2 * Copyright (C) 2004-2010 NXP Software 3 * Copyright (C) 2010 The Android Open Source Project 4 * 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 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 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. 16 */ 17 18 /************************************************************************/ 19 /* */ 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)*/ 24 /* */ 25 /************************************************************************/ 26 27 /*######################################################################################*/ 28 /* Include files */ 29 /*######################################################################################*/ 30 31 #include "ScalarArithmetic.h" 32 33 34 /**************************************************************************************** 35 * Name : dB_to_Lin32() 36 * Input : Signed 16-bit integer 37 * MSB (16) = sign bit 38 * (15->05) = integer part 39 * (04->01) = decimal part 40 * Output : Signed 32-bit integer 41 * MSB (32) = sign bit 42 * (31->16) = integer part 43 * (15->01) = decimal part 44 * Returns : Lin value format 1.16.15 45 * Description : 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 48 * with the equation: 49 * 50 * Correction = (Remainder / 1.5029) - (Remainder^2 / 6) 51 * 52 * The two coefficients are scaled from 0x40000000 in 96 steps and calculated 53 * as follows: 54 * 55 * FIRST_COEF = 0x80000000 / (96 * 1.5029) 56 * SECOND_COEF = 0x80000000 / (96^2 * 6) 57 * 58 ****************************************************************************************/ 59 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 */ 66 67 LVM_INT32 dB_to_Lin32(LVM_INT16 db_fix) 68 { 69 LVM_INT32 Lin_val_32; 70 LVM_INT16 Shift; 71 LVM_INT32 Remain; 72 73 74 /* 75 * Check sign of the input 76 */ 77 if (db_fix<0) 78 { 79 if (db_fix > -MAX_VALUE) 80 { 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)); 85 } 86 else 87 { 88 Lin_val_32 = 0; 89 } 90 } 91 else 92 { 93 if (db_fix < MAX_VALUE) 94 { 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)); 99 } 100 else 101 { 102 Lin_val_32 = 0x7FFFFFFF; 103 } 104 } 105 106 107 return Lin_val_32; /* format 1.16.15 */ 108 } 109 110
