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/****************************************************************************************
19Portions 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)
26Permission to distribute, modify and use this file under the standard license
27terms listed above has been obtained from the copyright holder.
28****************************************************************************************/
29/*
30
31 Filename: /audio/gsm_amr/c/src/shr.c
32
33------------------------------------------------------------------------------
34 REVISION HISTORY
35
36 Description: Created separate file for the shr function. Sync'ed up with
37          the current template and fixed tabs.
38
39 Description: 1. Modified code by seperating var2=0 condition.
40              2. Changed Input range definitions.
41
42 Description: Made changes based on review meeting.
43              1. Changed Overflow definition.
44              2. Removed pseudo-code.
45              3. Deleted (var2>15&&var1!=0) condition.
46              4. Moved var2>0 condition in front of var2<0 condition.
47
48 Description: Changed the function prototype to pass in a pointer to the
49              overflow flag instead of using global data.
50
51 Description: Made changes per formal review. Updated template.
52              Removed code that updates MOPS counter.
53              Changed parameter name from "overflow" and "pOverflow".
54              Optimized code by eliminating unnecessary typecasting.
55              Filled in the PSEUDO CODE section
56
57 Description: Further optimized typecasting for overflow case
58
59 Who:                       Date:
60 Description:
61------------------------------------------------------------------------------
62------------------------------------------------------------------------------
63 MODULE DESCRIPTION
64 Shift right function with overflow control
65------------------------------------------------------------------------------
66*/
67
68/*----------------------------------------------------------------------------
69; INCLUDES
70----------------------------------------------------------------------------*/
71#include    "basic_op.h"
72
73/*----------------------------------------------------------------------------
74; MACROS
75; [Define module specific macros here]
76----------------------------------------------------------------------------*/
77
78/*----------------------------------------------------------------------------
79; DEFINES
80; [Include all pre-processor statements here. Include conditional
81; compile variables also.]
82----------------------------------------------------------------------------*/
83
84/*----------------------------------------------------------------------------
85; LOCAL FUNCTION DEFINITIONS
86; [List function prototypes here]
87----------------------------------------------------------------------------*/
88
89/*----------------------------------------------------------------------------
90; LOCAL VARIABLE DEFINITIONS
91; [Variable declaration - defined here and used outside this module]
92----------------------------------------------------------------------------*/
93
94
95/*
96------------------------------------------------------------------------------
97 FUNCTION NAME: shr
98------------------------------------------------------------------------------
99 INPUT AND OUTPUT DEFINITIONS
100
101 Inputs:
102    var1 = 16 bit short signed integer (Word16) whose value falls in
103           the range : 0xffff 8000 <= var1 <= 0x0000 7fff.
104
105    var2 = 16 bit short signed integer (Word16) whose value falls in
106           the range : 0xffff 8000 <= var2 <= 0x0000 7fff.
107
108    pOverflow = pointer to overflow (Flag)
109
110 Outputs:
111    pOverflow -> 1 if the shift operation resulted in overflow
112
113 Returns:
114    product = Shifted result limited to 16 bits (Word16)
115
116 Global Variables Used:
117    None
118
119 Local Variables Needed:
120    None
121
122------------------------------------------------------------------------------
123 FUNCTION DESCRIPTION
124
125 This function arithmetically shifts the 16 bit input var1 right var2 positions
126 with sign extension. If var2 is negative, arithmetically shift var1 left by
127 -var2 with sign extension. Saturate the result in case of underflows or
128 overflows.
129
130------------------------------------------------------------------------------
131 REQUIREMENTS
132 None
133------------------------------------------------------------------------------
134 REFERENCES
135
136 [1] shr() function in basic_op2.c,  UMTS GSM AMR speech codec, R99 -
137 Version 3.2.0, March 2, 2001
138
139------------------------------------------------------------------------------
140 PSEUDO-CODE
141
142Word16 shr_std (Word16 var1, Word16 var2)
143{
144    Word16 var_out;
145
146    if (var2 < 0)
147    {
148        if (var2 < -16)
149            var2 = -16;
150        var_out = shl_std (var1, -var2);
151#if (WMOPS)
152        mult_stdiCounter[currCounter].shl_std--;
153#endif
154    }
155    else
156    {
157        if (var2 >= 15)
158        {
159            var_out = (var1 < 0) ? -1 : 0;
160        }
161        else
162        {
163            if (var1 < 0)
164            {
165                var_out = ~((~var1) >> var2);
166            }
167            else
168            {
169                var_out = var1 >> var2;
170            }
171        }
172    }
173
174#if (WMOPS)
175    mult_stdiCounter[currCounter].shr_std++;
176#endif
177    return (var_out);
178}
179------------------------------------------------------------------------------
180 RESOURCES USED [optional]
181
182 When the code is written for a specific target processor the
183 the resources used should be documented below.
184
185 HEAP MEMORY USED: x bytes
186
187 STACK MEMORY USED: x bytes
188
189 CLOCK CYCLES: (cycle count equation for this function) + (variable
190                used to represent cycle count for each subroutine
191                called)
192     where: (cycle count variable) = cycle count for [subroutine
193                                     name]
194
195------------------------------------------------------------------------------
196 CAUTION [optional]
197 [State any special notes, constraints or cautions for users of this function]
198
199------------------------------------------------------------------------------
200*/
201
202/*----------------------------------------------------------------------------
203; FUNCTION CODE
204----------------------------------------------------------------------------*/
205Word16 shr(register Word16 var1, register Word16 var2, Flag *pOverflow)
206{
207    register Word16 result;
208    register Word32 temp_res;
209
210    if (var2 != 0)
211    {
212        if (var2 > 0)
213        {
214            if (var2 >= 15)
215            {
216                result = ((var1 < 0) ? -1 : 0);
217            }
218            else
219            {
220                if (var1 < 0)
221                {
222                    result = (~((~var1) >> var2));
223                }
224                else
225                {
226                    result = (var1 >> var2);
227                }
228            }
229        }
230        else
231        {
232            if (var2 < -16)
233            {
234                var2 = -16;
235            }
236
237            var2 = -var2;   /* Shift right negative is equivalent */
238            /*   to shifting left positive.       */
239
240            temp_res = ((Word32) var1) << var2;
241            result = (Word16)(temp_res);
242
243            if (temp_res != (Word32) result)
244            {
245                *pOverflow = 1;
246                result = ((var1 > 0) ? MAX_16 : MIN_16);
247            }
248        }
249
250    }
251    else
252    {
253        result = var1;
254    }
255
256    return (result);
257}
258
259