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/sqrt_l.c 32 33 ------------------------------------------------------------------------------ 34 REVISION HISTORY 35 36 37 Description: Updated template. Changed function interface to pass in a 38 pointer to overflow flag into the function instead of using a 39 global flag. Changed name of an input pointer from "exp" to "pExp" 40 for clarity. Removed inclusion of unwanted header files. 41 42 Description: Removed inclusion of sqrt_l.tab file. Changed the array name 43 "table" to "sqrt_l_tbl". Fixed typos. 44 45 Who: Date: 46 Description: 47 48 ------------------------------------------------------------------------------ 49 */ 50 51 /*---------------------------------------------------------------------------- 52 ; INCLUDES 53 ----------------------------------------------------------------------------*/ 54 #include "sqrt_l.h" 55 #include "typedef.h" 56 #include "basic_op.h" 57 58 /*---------------------------------------------------------------------------- 59 ; MACROS 60 ; Define module specific macros here 61 ----------------------------------------------------------------------------*/ 62 63 64 /*---------------------------------------------------------------------------- 65 ; DEFINES 66 ; Include all pre-processor statements here. Include conditional 67 ; compile variables also. 68 ----------------------------------------------------------------------------*/ 69 70 71 /*---------------------------------------------------------------------------- 72 ; LOCAL FUNCTION DEFINITIONS 73 ; Function Prototype declaration 74 ----------------------------------------------------------------------------*/ 75 76 77 /*---------------------------------------------------------------------------- 78 ; LOCAL STORE/BUFFER/POINTER DEFINITIONS 79 ; Variable declaration - defined here and used outside this module 80 ----------------------------------------------------------------------------*/ 81 82 83 /* 84 ------------------------------------------------------------------------------ 85 FUNCTION NAME: sqrt_l_exp 86 ------------------------------------------------------------------------------ 87 INPUT AND OUTPUT DEFINITIONS 88 89 Inputs: 90 L_x = input value (Word32) 91 pExp = pointer to right shift to be applied to result 92 pOverflow = pointer to overflow flag 93 94 Outputs: 95 pOverflow -> if the Inv_sqrt operation resulted in an overflow. 96 97 Returns: 98 L_y = squareroot of L_x (Word32) 99 100 Global Variables Used: 101 None. 102 103 Local Variables Needed: 104 None. 105 106 ------------------------------------------------------------------------------ 107 FUNCTION DESCRIPTION 108 109 This function computes sqrt(L_x), where L_x is positive. 110 If L_var is negative or zero, the result is 0 111 112 The function sqrt(L_x) is approximated by a table and linear 113 interpolation. The square root is computed using the 114 following steps: 115 1- Normalization of L_x. 116 2- If exponent is even then shift right once. 117 3- exponent = exponent/2 118 4- i = bit25-b31 of L_x; 16<=i<=63 because of normalization. 119 5- a = bit10-b24 120 6- i -=16 121 7- L_y = table[i]<<16 - (table[i] - table[i+1]) * a * 2 122 8- return L_y and exponent so caller can do denormalization 123 124 ------------------------------------------------------------------------------ 125 REQUIREMENTS 126 127 None. 128 129 ------------------------------------------------------------------------------ 130 REFERENCES 131 132 sqrt_l.c, UMTS GSM AMR speech codec, R99 - Version 3.2.0, March 2, 2001 133 134 ------------------------------------------------------------------------------ 135 PSEUDO-CODE 136 137 Word32 sqrt_l_exp ( // o : output value 138 Word32 L_x, // i : input value 139 Word16 *exp // o : right shift to be applied to result 140 ) 141 { 142 143 // y = sqrt(x) 144 // x = f * 2^-e, 0.5 <= f < 1 (normalization) 145 // y = sqrt(f) * 2^(-e/2) 146 // 147 // a) e = 2k --> y = sqrt(f) * 2^-k (k = e div 2, 148 // 0.707 <= sqrt(f) < 1) 149 // b) e = 2k+1 --> y = sqrt(f/2) * 2^-k (k = e div 2, 150 0.5 <= sqrt(f/2) < 0.707) 151 152 153 Word16 e, i, a, tmp; 154 Word32 L_y; 155 156 if (L_x <= (Word32) 0) 157 { 158 *exp = 0; 159 return (Word32) 0; 160 } 161 162 * The reference ETSI code uses a global Overflow flag. In the actual 163 * implementation a pointer to the overflow flag is passed into the function. 164 * This pointer is in turn passed into the basic math functions such as add(), 165 * L_shl(), L_shr(), sub() called by this module. 166 167 e = norm_l (L_x) & 0xFFFE; // get next lower EVEN norm. exp 168 L_x = L_shl (L_x, e); // L_x is normalized to [0.25..1) 169 *exp = e; // return 2*exponent (or Q1) 170 171 L_x = L_shr (L_x, 9); 172 i = extract_h (L_x); // Extract b25-b31, 16 <= i <= 63 173 because of normalization 174 L_x = L_shr (L_x, 1); 175 a = extract_l (L_x); // Extract b10-b24 176 a = a & (Word16) 0x7fff; 177 178 i = sub (i, 16); // 0 <= i <= 47 179 180 L_y = L_deposit_h (table[i]); // table[i] << 16 181 tmp = sub (table[i], table[i + 1]); // table[i] - table[i+1]) 182 L_y = L_msu (L_y, tmp, a); // L_y -= tmp*a*2 183 184 return (L_y); 185 } 186 187 ------------------------------------------------------------------------------ 188 RESOURCES USED [optional] 189 190 When the code is written for a specific target processor the 191 the resources used should be documented below. 192 193 HEAP MEMORY USED: x bytes 194 195 STACK MEMORY USED: x bytes 196 197 CLOCK CYCLES: (cycle count equation for this function) + (variable 198 used to represent cycle count for each subroutine 199 called) 200 where: (cycle count variable) = cycle count for [subroutine 201 name] 202 203 ------------------------------------------------------------------------------ 204 CAUTION [optional] 205 [State any special notes, constraints or cautions for users of this function] 206 207 ------------------------------------------------------------------------------ 208 */ 209 210 Word32 sqrt_l_exp( /* o : output value, Q31 */ 211 Word32 L_x, /* i : input value, Q31 */ 212 Word16 *pExp, /* o : right shift to be applied to result, Q1 */ 213 Flag *pOverflow /* i : pointer to overflow flag */ 214 ) 215 216 { 217 Word16 e; 218 Word16 i; 219 Word16 a; 220 Word16 tmp; 221 Word32 L_y; 222 223 /* 224 y = sqrt(x) 225 x = f * 2^-e, 0.5 <= f < 1 (normalization) 226 y = sqrt(f) * 2^(-e/2) 227 a) e = 2k --> y = sqrt(f) * 2^-k (k = e div 2, 228 0.707 <= sqrt(f) < 1) 229 b) e = 2k+1 --> y = sqrt(f/2) * 2^-k (k = e div 2, 230 0.5 <= sqrt(f/2) < 0.707) 231 */ 232 233 if (L_x <= (Word32) 0) 234 { 235 *pExp = 0; 236 return (Word32) 0; 237 } 238 239 e = norm_l(L_x) & 0xFFFE; /* get next lower EVEN norm. exp */ 240 L_x = L_shl(L_x, e, pOverflow); /* L_x is normalized to [0.25..1) */ 241 *pExp = e; /* return 2*exponent (or Q1) */ 242 243 L_x >>= 10; 244 i = (Word16)(L_x >> 15) & 63; /* Extract b25-b31, 16<= i <=63 */ 245 /* because of normalization */ 246 247 a = (Word16)(L_x); /* Extract b10-b24 */ 248 a &= (Word16) 0x7fff; 249 250 if (i > 15) 251 { 252 i -= 16; /* 0 <= i <= 47 */ 253 } 254 255 L_y = L_deposit_h(sqrt_l_tbl[i]); /* sqrt_l_tbl[i] << 16 */ 256 257 /* sqrt_l_tbl[i] - sqrt_l_tbl[i+1]) */ 258 tmp = sub(sqrt_l_tbl[i], sqrt_l_tbl[i + 1], pOverflow); 259 260 L_y = L_msu(L_y, tmp, a, pOverflow); /* L_y -= tmp*a*2 */ 261 262 /* L_y = L_shr (L_y, *exp); */ /* denormalization done by caller */ 263 264 return (L_y); 265 } 266 267
