14f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber/* ------------------------------------------------------------------ 24f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber * Copyright (C) 1998-2009 PacketVideo 34f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber * 44f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber * Licensed under the Apache License, Version 2.0 (the "License"); 54f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber * you may not use this file except in compliance with the License. 64f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber * You may obtain a copy of the License at 74f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber * 84f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber * http://www.apache.org/licenses/LICENSE-2.0 94f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber * 104f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber * Unless required by applicable law or agreed to in writing, software 114f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber * distributed under the License is distributed on an "AS IS" BASIS, 124f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either 134f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber * express or implied. 144f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber * See the License for the specific language governing permissions 154f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber * and limitations under the License. 164f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber * ------------------------------------------------------------------- 174f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber */ 184f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber/**************************************************************************************** 194f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas HuberPortions of this file are derived from the following 3GPP standard: 204f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 214f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 3GPP TS 26.073 224f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber ANSI-C code for the Adaptive Multi-Rate (AMR) speech codec 234f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Available from http://www.3gpp.org 244f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 254f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber(C) 2004, 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TTA, TTC) 264f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas HuberPermission to distribute, modify and use this file under the standard license 274f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huberterms listed above has been obtained from the copyright holder. 284f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber****************************************************************************************/ 294f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber/* 304f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 314f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Pathname: ./audio/gsm-amr/c/src/log2_norm.c 324f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 334f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber------------------------------------------------------------------------------ 344f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber REVISION HISTORY 354f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 364f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Description: Created separate file for Log2_norm function. 374f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 384f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Description: Synchronized file with UMTS version 3.2.0. Updated coding 394f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber template. Removed unnecessary include file. 404f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 414f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Description: Made the following changes per comments from Phase 2/3 review: 424f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1. Modified code to improve performance. 434f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 2. Fixed typecasting issue with TI C compiler. 444f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 3. Added more comments to the code. 454f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 464f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Description: Removed unnecessary line of code (line 208). 474f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 484f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Description: Removed inclusion of "log2.tab" 494f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 504f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Who: Date: 514f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Description: 524f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 534f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber------------------------------------------------------------------------------ 544f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber*/ 554f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 564f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber/*---------------------------------------------------------------------------- 574f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber; INCLUDES 584f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber----------------------------------------------------------------------------*/ 594f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber#include "log2_norm.h" 604f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 614f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber/*---------------------------------------------------------------------------- 624f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber; MACROS 634f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber; Define module specific macros here 644f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber----------------------------------------------------------------------------*/ 654f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 664f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 674f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber/*---------------------------------------------------------------------------- 684f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber; DEFINES 694f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber; Include all pre-processor statements here. Include conditional 704f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber; compile variables also. 714f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber----------------------------------------------------------------------------*/ 724f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 734f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber/*---------------------------------------------------------------------------- 744f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber; LOCAL FUNCTION DEFINITIONS 754f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber; Function Prototype declaration 764f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber----------------------------------------------------------------------------*/ 774f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 784f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber/*---------------------------------------------------------------------------- 794f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber; LOCAL STORE/BUFFER/POINTER DEFINITIONS 804f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber; Variable declaration - defined here and used outside this module 814f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber----------------------------------------------------------------------------*/ 824f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 834f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 844f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber/* 854f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber------------------------------------------------------------------------------ 864f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber FUNCTION NAME: Log2_norm 874f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber------------------------------------------------------------------------------ 884f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber INPUT AND OUTPUT DEFINITIONS 894f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 904f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Inputs: 914f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber L_x = normalized input value of type Word32 924f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber exp = number of shifts required to normalize L_x; it is of type Word16 934f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber exponent = pointer to the integer part of Log2 (of type Word16) 944f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber whose valid range is: 0 <= value <= 30 954f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber fraction = pointer to the fractional part of Log2 (of type Word16) 964f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber whose valid range is: 0 <= value < 1 974f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 984f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Outputs: 994f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber exponent points to the newly calculated integer part of Log2 1004f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber fraction points to the newly calculated fractional part of Log2 1014f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1024f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Returns: 1034f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber None 1044f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1054f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Global Variables Used: 1064f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber None 1074f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1084f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Local Variables Needed: 1094f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber table = Log2 table of constants of type Word16 1104f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1114f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber------------------------------------------------------------------------------ 1124f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber FUNCTION DESCRIPTION 1134f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1144f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber The function Log2(L_x) calculates the logarithm of the normalized input 1154f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber buffer L_x. The logarithm is approximated by a table and linear 1164f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber interpolation. The following steps are used to compute Log2(L_x): 1174f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1184f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1. exponent = 30 - norm_exponent 1194f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 2. i = bit25-b31 of L_x; 32<=i<=63 (because of normalization). 1204f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 3. a = bit10-b24 1214f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 4. i = i - 32 1224f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 5. fraction = table[i]<<16 - (table[i] - table[i+1]) * a * 2 1234f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1244f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber------------------------------------------------------------------------------ 1254f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber REQUIREMENTS 1264f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1274f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber None 1284f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1294f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber------------------------------------------------------------------------------ 1304f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber REFERENCES 1314f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1324f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber log2.c, UMTS GSM AMR speech codec, R99 - Version 3.2.0, March 2, 2001 1334f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1344f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber------------------------------------------------------------------------------ 1354f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber PSEUDO-CODE 1364f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1374f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Hubervoid Log2_norm ( 1384f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Word32 L_x, // (i) : input value (normalized) 1394f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Word16 exp, // (i) : norm_l (L_x) 1404f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Word16 *exponent, // (o) : Integer part of Log2. (range: 0<=val<=30) 1414f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Word16 *fraction // (o) : Fractional part of Log2. (range: 0<=val<1) 1424f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber) 1434f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber{ 1444f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Word16 i, a, tmp; 1454f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Word32 L_y; 1464f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1474f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber if (L_x <= (Word32) 0) 1484f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber { 1494f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber *exponent = 0; 1504f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber *fraction = 0; 1514f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber return; 1524f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber } 1534f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1544f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber *exponent = sub (30, exp); 1554f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1564f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber L_x = L_shr (L_x, 9); 1574f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber i = extract_h (L_x); // Extract b25-b31 1584f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber L_x = L_shr (L_x, 1); 1594f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber a = extract_l (L_x); // Extract b10-b24 of fraction 1604f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber a = a & (Word16) 0x7fff; 1614f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1624f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber i = sub (i, 32); 1634f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1644f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber L_y = L_deposit_h (table[i]); // table[i] << 16 1654f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber tmp = sub (table[i], table[i + 1]); // table[i] - table[i+1] 1664f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber L_y = L_msu (L_y, tmp, a); // L_y -= tmp*a*2 1674f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1684f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber *fraction = extract_h (L_y); 1694f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1704f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber return; 1714f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber} 1724f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1734f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber------------------------------------------------------------------------------ 1744f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber RESOURCES USED [optional] 1754f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1764f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber When the code is written for a specific target processor the 1774f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber the resources used should be documented below. 1784f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1794f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber HEAP MEMORY USED: x bytes 1804f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1814f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber STACK MEMORY USED: x bytes 1824f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1834f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber CLOCK CYCLES: (cycle count equation for this function) + (variable 1844f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber used to represent cycle count for each subroutine 1854f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber called) 1864f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber where: (cycle count variable) = cycle count for [subroutine 1874f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber name] 1884f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1894f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber------------------------------------------------------------------------------ 1904f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber CAUTION [optional] 1914f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber [State any special notes, constraints or cautions for users of this function] 1924f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1934f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber------------------------------------------------------------------------------ 1944f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber*/ 1954f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 1964f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Hubervoid Log2_norm( 1974f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Word32 L_x, /* (i) : input value (normalized) */ 1984f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Word16 exp, /* (i) : norm_l (L_x) */ 1994f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Word16 *exponent, /* (o) : Integer part of Log2. (range: 0<=val<=30)*/ 2004f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Word16 *fraction /* (o) : Fractional part of Log2. (range: 0<=val<1) */ 2014f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber) 2024f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber{ 2034f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Word16 i, a, tmp; 2044f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber Word32 L_y; 2054f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 2064f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber if (L_x <= (Word32) 0) 2074f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber { 2084f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber *exponent = 0; 2094f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber *fraction = 0; 2104f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber } 2114f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber else 2124f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber { 2134f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber /* Calculate exponent portion of Log2 */ 2144f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber *exponent = 30 - exp; 2154f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 2164f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber /* At this point, L_x > 0 */ 2174f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber /* Shift L_x to the right by 10 to extract bits 10-31, */ 2184f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber /* which is needed to calculate fractional part of Log2 */ 2194f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber L_x >>= 10; 2204f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber i = (Word16)(L_x >> 15); /* Extract b25-b31 */ 2214f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber a = L_x & 0x7fff; /* Extract b10-b24 of fraction */ 2224f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 2234f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber /* Calculate table index -> subtract by 32 is done for */ 2244f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber /* proper table indexing, since 32<=i<=63 (due to normalization) */ 2254f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber i -= 32; 2264f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 2274f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber /* Fraction part of Log2 is approximated by using table[] */ 2284f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber /* and linear interpolation, i.e., */ 2294f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber /* fraction = table[i]<<16 - (table[i] - table[i+1]) * a * 2 */ 2304f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber L_y = (Word32) log2_tbl[i] << 16; /* table[i] << 16 */ 2314f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber tmp = log2_tbl[i] - log2_tbl[i + 1]; /* table[i] - table[i+1] */ 2324f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber L_y -= (((Word32) tmp) * a) << 1; /* L_y -= tmp*a*2 */ 2334f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 2344f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber *fraction = (Word16)(L_y >> 16); 2354f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber } 2364f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber 2374f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber return; 2384f1efc098cb5791c3e9f483f2af84aef70d2d0a0Andreas Huber} 239