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/* ------------------------------------------------------------------
* Copyright (C) 1998-2009 PacketVideo
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
* express or implied.
* See the License for the specific language governing permissions
* and limitations under the License.
* -------------------------------------------------------------------
*/
/****************************************************************************************
Portions of this file are derived from the following 3GPP standard:
3GPP TS 26.073
ANSI-C code for the Adaptive Multi-Rate (AMR) speech codec
Available from http://www.3gpp.org
(C) 2004, 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TTA, TTC)
Permission to distribute, modify and use this file under the standard license
terms listed above has been obtained from the copyright holder.
****************************************************************************************/
/*
Filename: /audio/gsm_amr/c/src/shr.c
------------------------------------------------------------------------------
REVISION HISTORY
Description: Created separate file for the shr function. Sync'ed up with
the current template and fixed tabs.
Description: 1. Modified code by seperating var2=0 condition.
2. Changed Input range definitions.
Description: Made changes based on review meeting.
1. Changed Overflow definition.
2. Removed pseudo-code.
3. Deleted (var2>15&&var1!=0) condition.
4. Moved var2>0 condition in front of var2<0 condition.
Description: Changed the function prototype to pass in a pointer to the
overflow flag instead of using global data.
Description: Made changes per formal review. Updated template.
Removed code that updates MOPS counter.
Changed parameter name from "overflow" and "pOverflow".
Optimized code by eliminating unnecessary typecasting.
Filled in the PSEUDO CODE section
Description: Further optimized typecasting for overflow case
Who: Date:
Description:
------------------------------------------------------------------------------
------------------------------------------------------------------------------
MODULE DESCRIPTION
Shift right function with overflow control
------------------------------------------------------------------------------
*/
/*----------------------------------------------------------------------------
; INCLUDES
----------------------------------------------------------------------------*/
#include "basic_op.h"
/*----------------------------------------------------------------------------
; MACROS
; [Define module specific macros here]
----------------------------------------------------------------------------*/
/*----------------------------------------------------------------------------
; DEFINES
; [Include all pre-processor statements here. Include conditional
; compile variables also.]
----------------------------------------------------------------------------*/
/*----------------------------------------------------------------------------
; LOCAL FUNCTION DEFINITIONS
; [List function prototypes here]
----------------------------------------------------------------------------*/
/*----------------------------------------------------------------------------
; LOCAL VARIABLE DEFINITIONS
; [Variable declaration - defined here and used outside this module]
----------------------------------------------------------------------------*/
/*
------------------------------------------------------------------------------
FUNCTION NAME: shr
------------------------------------------------------------------------------
INPUT AND OUTPUT DEFINITIONS
Inputs:
var1 = 16 bit short signed integer (Word16) whose value falls in
the range : 0xffff 8000 <= var1 <= 0x0000 7fff.
var2 = 16 bit short signed integer (Word16) whose value falls in
the range : 0xffff 8000 <= var2 <= 0x0000 7fff.
pOverflow = pointer to overflow (Flag)
Outputs:
pOverflow -> 1 if the shift operation resulted in overflow
Returns:
product = Shifted result limited to 16 bits (Word16)
Global Variables Used:
None
Local Variables Needed:
None
------------------------------------------------------------------------------
FUNCTION DESCRIPTION
This function arithmetically shifts the 16 bit input var1 right var2 positions
with sign extension. If var2 is negative, arithmetically shift var1 left by
-var2 with sign extension. Saturate the result in case of underflows or
overflows.
------------------------------------------------------------------------------
REQUIREMENTS
None
------------------------------------------------------------------------------
REFERENCES
[1] shr() function in basic_op2.c, UMTS GSM AMR speech codec, R99 -
Version 3.2.0, March 2, 2001
------------------------------------------------------------------------------
PSEUDO-CODE
Word16 shr_std (Word16 var1, Word16 var2)
{
Word16 var_out;
if (var2 < 0)
{
if (var2 < -16)
var2 = -16;
var_out = shl_std (var1, -var2);
#if (WMOPS)
mult_stdiCounter[currCounter].shl_std--;
#endif
}
else
{
if (var2 >= 15)
{
var_out = (var1 < 0) ? -1 : 0;
}
else
{
if (var1 < 0)
{
var_out = ~((~var1) >> var2);
}
else
{
var_out = var1 >> var2;
}
}
}
#if (WMOPS)
mult_stdiCounter[currCounter].shr_std++;
#endif
return (var_out);
}
------------------------------------------------------------------------------
RESOURCES USED [optional]
When the code is written for a specific target processor the
the resources used should be documented below.
HEAP MEMORY USED: x bytes
STACK MEMORY USED: x bytes
CLOCK CYCLES: (cycle count equation for this function) + (variable
used to represent cycle count for each subroutine
called)
where: (cycle count variable) = cycle count for [subroutine
name]
------------------------------------------------------------------------------
CAUTION [optional]
[State any special notes, constraints or cautions for users of this function]
------------------------------------------------------------------------------
*/
/*----------------------------------------------------------------------------
; FUNCTION CODE
----------------------------------------------------------------------------*/
Word16 shr(Word16 var1, Word16 var2, Flag *pOverflow)
{
Word16 result;
Word32 temp_res;
if (var2 != 0)
{
if (var2 > 0)
{
if (var2 >= 15)
{
result = ((var1 < 0) ? -1 : 0);
}
else
{
if (var1 < 0)
{
result = (~((~var1) >> var2));
}
else
{
result = (var1 >> var2);
}
}
}
else
{
if (var2 < -16)
{
var2 = -16;
}
var2 = -var2; /* Shift right negative is equivalent */
/* to shifting left positive. */
temp_res = ((Word32) var1) << var2;
result = (Word16)(temp_res);
if (temp_res != (Word32) result)
{
*pOverflow = 1;
result = ((var1 > 0) ? MAX_16 : MIN_16);
}
}
}
else
{
result = var1;
}
return (result);
}
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