1 /* ------------------------------------------------------------------ 2 * Copyright (C) 1998-2009 PacketVideo 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either 13 * express or implied. 14 * See the License for the specific language governing permissions 15 * and limitations under the License. 16 * ------------------------------------------------------------------- 17 */ 18 /**************************************************************************************** 19 Portions of this file are derived from the following 3GPP standard: 20 21 3GPP TS 26.073 22 ANSI-C code for the Adaptive Multi-Rate (AMR) speech codec 23 Available from http://www.3gpp.org 24 25 (C) 2004, 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TTA, TTC) 26 Permission to distribute, modify and use this file under the standard license 27 terms listed above has been obtained from the copyright holder. 28 ****************************************************************************************/ 29 /* 30 31 Pathname: ./audio/gsm-amr/c/src/log2_norm.c 32 33 ------------------------------------------------------------------------------ 34 REVISION HISTORY 35 36 Description: Created separate file for Log2_norm function. 37 38 Description: Synchronized file with UMTS version 3.2.0. Updated coding 39 template. Removed unnecessary include file. 40 41 Description: Made the following changes per comments from Phase 2/3 review: 42 1. Modified code to improve performance. 43 2. Fixed typecasting issue with TI C compiler. 44 3. Added more comments to the code. 45 46 Description: Removed unnecessary line of code (line 208). 47 48 Description: Removed inclusion of "log2.tab" 49 50 Who: Date: 51 Description: 52 53 ------------------------------------------------------------------------------ 54 */ 55 56 /*---------------------------------------------------------------------------- 57 ; INCLUDES 58 ----------------------------------------------------------------------------*/ 59 #include "log2_norm.h" 60 61 /*---------------------------------------------------------------------------- 62 ; MACROS 63 ; Define module specific macros here 64 ----------------------------------------------------------------------------*/ 65 66 67 /*---------------------------------------------------------------------------- 68 ; DEFINES 69 ; Include all pre-processor statements here. Include conditional 70 ; compile variables also. 71 ----------------------------------------------------------------------------*/ 72 73 /*---------------------------------------------------------------------------- 74 ; LOCAL FUNCTION DEFINITIONS 75 ; Function Prototype declaration 76 ----------------------------------------------------------------------------*/ 77 78 /*---------------------------------------------------------------------------- 79 ; LOCAL STORE/BUFFER/POINTER DEFINITIONS 80 ; Variable declaration - defined here and used outside this module 81 ----------------------------------------------------------------------------*/ 82 83 84 /* 85 ------------------------------------------------------------------------------ 86 FUNCTION NAME: Log2_norm 87 ------------------------------------------------------------------------------ 88 INPUT AND OUTPUT DEFINITIONS 89 90 Inputs: 91 L_x = normalized input value of type Word32 92 exp = number of shifts required to normalize L_x; it is of type Word16 93 exponent = pointer to the integer part of Log2 (of type Word16) 94 whose valid range is: 0 <= value <= 30 95 fraction = pointer to the fractional part of Log2 (of type Word16) 96 whose valid range is: 0 <= value < 1 97 98 Outputs: 99 exponent points to the newly calculated integer part of Log2 100 fraction points to the newly calculated fractional part of Log2 101 102 Returns: 103 None 104 105 Global Variables Used: 106 None 107 108 Local Variables Needed: 109 table = Log2 table of constants of type Word16 110 111 ------------------------------------------------------------------------------ 112 FUNCTION DESCRIPTION 113 114 The function Log2(L_x) calculates the logarithm of the normalized input 115 buffer L_x. The logarithm is approximated by a table and linear 116 interpolation. The following steps are used to compute Log2(L_x): 117 118 1. exponent = 30 - norm_exponent 119 2. i = bit25-b31 of L_x; 32<=i<=63 (because of normalization). 120 3. a = bit10-b24 121 4. i = i - 32 122 5. fraction = table[i]<<16 - (table[i] - table[i+1]) * a * 2 123 124 ------------------------------------------------------------------------------ 125 REQUIREMENTS 126 127 None 128 129 ------------------------------------------------------------------------------ 130 REFERENCES 131 132 log2.c, UMTS GSM AMR speech codec, R99 - Version 3.2.0, March 2, 2001 133 134 ------------------------------------------------------------------------------ 135 PSEUDO-CODE 136 137 void Log2_norm ( 138 Word32 L_x, // (i) : input value (normalized) 139 Word16 exp, // (i) : norm_l (L_x) 140 Word16 *exponent, // (o) : Integer part of Log2. (range: 0<=val<=30) 141 Word16 *fraction // (o) : Fractional part of Log2. (range: 0<=val<1) 142 ) 143 { 144 Word16 i, a, tmp; 145 Word32 L_y; 146 147 if (L_x <= (Word32) 0) 148 { 149 *exponent = 0; 150 *fraction = 0; 151 return; 152 } 153 154 *exponent = sub (30, exp); 155 156 L_x = L_shr (L_x, 9); 157 i = extract_h (L_x); // Extract b25-b31 158 L_x = L_shr (L_x, 1); 159 a = extract_l (L_x); // Extract b10-b24 of fraction 160 a = a & (Word16) 0x7fff; 161 162 i = sub (i, 32); 163 164 L_y = L_deposit_h (table[i]); // table[i] << 16 165 tmp = sub (table[i], table[i + 1]); // table[i] - table[i+1] 166 L_y = L_msu (L_y, tmp, a); // L_y -= tmp*a*2 167 168 *fraction = extract_h (L_y); 169 170 return; 171 } 172 173 ------------------------------------------------------------------------------ 174 RESOURCES USED [optional] 175 176 When the code is written for a specific target processor the 177 the resources used should be documented below. 178 179 HEAP MEMORY USED: x bytes 180 181 STACK MEMORY USED: x bytes 182 183 CLOCK CYCLES: (cycle count equation for this function) + (variable 184 used to represent cycle count for each subroutine 185 called) 186 where: (cycle count variable) = cycle count for [subroutine 187 name] 188 189 ------------------------------------------------------------------------------ 190 CAUTION [optional] 191 [State any special notes, constraints or cautions for users of this function] 192 193 ------------------------------------------------------------------------------ 194 */ 195 196 void Log2_norm( 197 Word32 L_x, /* (i) : input value (normalized) */ 198 Word16 exp, /* (i) : norm_l (L_x) */ 199 Word16 *exponent, /* (o) : Integer part of Log2. (range: 0<=val<=30)*/ 200 Word16 *fraction /* (o) : Fractional part of Log2. (range: 0<=val<1) */ 201 ) 202 { 203 Word16 i, a, tmp; 204 Word32 L_y; 205 206 if (L_x <= (Word32) 0) 207 { 208 *exponent = 0; 209 *fraction = 0; 210 } 211 else 212 { 213 /* Calculate exponent portion of Log2 */ 214 *exponent = 30 - exp; 215 216 /* At this point, L_x > 0 */ 217 /* Shift L_x to the right by 10 to extract bits 10-31, */ 218 /* which is needed to calculate fractional part of Log2 */ 219 L_x >>= 10; 220 i = (Word16)(L_x >> 15); /* Extract b25-b31 */ 221 a = L_x & 0x7fff; /* Extract b10-b24 of fraction */ 222 223 /* Calculate table index -> subtract by 32 is done for */ 224 /* proper table indexing, since 32<=i<=63 (due to normalization) */ 225 i -= 32; 226 227 /* Fraction part of Log2 is approximated by using table[] */ 228 /* and linear interpolation, i.e., */ 229 /* fraction = table[i]<<16 - (table[i] - table[i+1]) * a * 2 */ 230 L_y = (Word32) log2_tbl[i] << 16; /* table[i] << 16 */ 231 tmp = log2_tbl[i] - log2_tbl[i + 1]; /* table[i] - table[i+1] */ 232 L_y -= (((Word32) tmp) * a) << 1; /* L_y -= tmp*a*2 */ 233 234 *fraction = (Word16)(L_y >> 16); 235 } 236 237 return; 238 } 239
