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 Filename: /audio/gsm_amr/c/src/sub.c 32 33 ------------------------------------------------------------------------------ 34 REVISION HISTORY 35 36 Description: Created separate file for the sub function. Sync'ed up with the 37 current template and fixed tabs. 38 39 Description: Changed all occurrences of L_diff to diff, deleted "short" in 40 the definition of var1 and var2, and fixed the range values. 41 42 Description: Changed function prototype passing in a pointer to overflow flag 43 instead of using global data. 44 45 Description: Changes made per formal review comments. 46 1. Changed the parameter name fron "overflow" to "pOverflow" 47 2. Updated template 48 3. Updated reference section 49 50 Description: Removed conditional code that updates WMOPS counter 51 52 Description: 53 1. Modified if-else structure to save cycles by processing 54 the most common case faster. 55 56 Who: Date: 57 Description: 58 59 ------------------------------------------------------------------------------ 60 MODULE DESCRIPTION 61 62 Subtraction function with overflow control 63 64 ------------------------------------------------------------------------------ 65 */ 66 67 /*---------------------------------------------------------------------------- 68 ; INCLUDES 69 ----------------------------------------------------------------------------*/ 70 #include "basic_op.h" 71 72 /*---------------------------------------------------------------------------- 73 ; MACROS 74 ; [Define module specific macros here] 75 ----------------------------------------------------------------------------*/ 76 77 /*---------------------------------------------------------------------------- 78 ; DEFINES 79 ; [Include all pre-processor statements here. Include conditional 80 ; compile variables also.] 81 ----------------------------------------------------------------------------*/ 82 83 /*---------------------------------------------------------------------------- 84 ; LOCAL FUNCTION DEFINITIONS 85 ; [List function prototypes here] 86 ----------------------------------------------------------------------------*/ 87 88 /*---------------------------------------------------------------------------- 89 ; LOCAL VARIABLE DEFINITIONS 90 ; [Variable declaration - defined here and used outside this module] 91 ----------------------------------------------------------------------------*/ 92 93 94 /* 95 ------------------------------------------------------------------------------ 96 FUNCTION NAME: sub 97 ------------------------------------------------------------------------------ 98 INPUT AND OUTPUT DEFINITIONS 99 100 Inputs: 101 var1 = 16 bit short signed integer (Word16) whose value falls in 102 the range : 0xffff 8000 <= var1 <= 0x0000 7fff. 103 104 var2 = 16 bit short signed integer (Word16) whose value falls in 105 the range : 0xffff 8000 <= var2 <= 0x0000 7fff. 106 107 pOverflow = pointer to overflow (Flag) 108 109 Outputs: 110 pOverflow -> 1 if the subtract operation resulted in overflow 111 112 Returns: 113 diff = 16-bit limited difference between var1 and var2 (Word16) 114 115 Global Variables Used: 116 None 117 118 Local Variables Needed: 119 None 120 121 ------------------------------------------------------------------------------ 122 FUNCTION DESCRIPTION 123 124 This function performs the subtraction (var1-var2) with overflow control and 125 saturation; the 16 bit result is set at +32767 when overflow occurs or at 126 -32768 when underflow occurs. 127 128 ------------------------------------------------------------------------------ 129 REQUIREMENTS 130 131 None 132 133 ------------------------------------------------------------------------------ 134 REFERENCES 135 136 [1] sub() function in basicop2.c, UMTS GSM AMR speech codec, R99 - 137 Version 3.2.0, March 2, 2001 138 139 ------------------------------------------------------------------------------ 140 141 PSEUDO-CODE 142 143 Word16 sub (Word16 var1, Word16 var2) 144 { 145 Word16 var_out; 146 Word32 diff; 147 148 diff = (Word32) var1 - var2; 149 150 * The reference ETSI code uses a global flag for Overflow inside the function 151 * saturate(). In the actual implementation a pointer to Overflow flag is passed 152 * in as a parameter to the function 153 154 var_out = saturate (diff); 155 156 #if (WMOPS) 157 multiCounter[currCounter].sub++; 158 #endif 159 160 return (var_out); 161 } 162 163 ------------------------------------------------------------------------------ 164 RESOURCES USED [optional] 165 166 When the code is written for a specific target processor the 167 the resources used should be documented below. 168 169 HEAP MEMORY USED: x bytes 170 171 STACK MEMORY USED: x bytes 172 173 CLOCK CYCLES: (cycle count equation for this function) + (variable 174 used to represent cycle count for each subroutine 175 called) 176 where: (cycle count variable) = cycle count for [subroutine 177 name] 178 179 ------------------------------------------------------------------------------ 180 CAUTION [optional] 181 [State any special notes, constraints or cautions for users of this function] 182 183 ------------------------------------------------------------------------------ 184 */ 185 186 /*---------------------------------------------------------------------------- 187 ; FUNCTION CODE 188 ----------------------------------------------------------------------------*/ 189 190 #ifdef __clang__ 191 __attribute__((no_sanitize("integer"))) 192 #endif 193 Word16 sub(Word16 var1, Word16 var2, Flag *pOverflow) 194 { 195 196 Word32 diff; 197 198 diff = (Word32) var1 - var2; 199 200 /* Saturate result (if necessary). */ 201 /* Replaced function call with in-line code */ 202 /* to conserve MIPS, i.e., var_out = saturate (diff) */ 203 204 205 if ((UWord32)(diff - 0xFFFF8000L) > 0x000FFFF) 206 { 207 if (diff > (Word32) 0x0007FFFL) 208 { 209 diff = MAX_16; 210 } 211 else 212 { 213 diff = MIN_16; 214 } 215 216 *pOverflow = 1; 217 } 218 219 220 return ((Word16) diff); 221 } 222
