div_s.cpp

实现3GPP的GSM中AMR语音的CODECS。

/* ------------------------------------------------------------------
 * Copyright (C) 2008 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.
****************************************************************************************/
/*
------------------------------------------------------------------------------


 Pathname: ./gsm-amr/c/src/div_s.c

     Date: 08/13/2000

------------------------------------------------------------------------------
 REVISION HISTORY

 Description: Created separate file for the div_s function. Sync'ed up
	      with the current template and fixed tabs.

 Description: Making changes based on review meeting.

 Description: Made changes based on P3 review meeting.

 Description: Changing abort() to exit(0).

 Description: Made the following changes
              1. Unrolled the division loop to make three comparison per
                 pass, using only five iterations of the loop and saving
                 shifts cycles

 Description:

------------------------------------------------------------------------------
 INPUT AND OUTPUT DEFINITIONS

 Inputs:
	var1 = 16 bit signed integer (Word16) whose value falls in
	       the range : 0x0000 <= var1 <= 0x7fff.
	var2 = 16 bit signed integer (Word16) whose value falls in
	       the range : 0x0000 <= var1 <= 0x7fff.

 Local Stores/Buffers/Pointers Needed:
	None

 Global Stores/Buffers/Pointers Needed:
	None

 Outputs:
	var_out = quotient of var1 divided by var2 (Word16)

 Pointers and Buffers Modified:
	None

 Local Stores Modified:
	None

 Global Stores Modified:
	None

------------------------------------------------------------------------------
 FUNCTION DESCRIPTION

 This function produces a result which is the fractional integer division of
 var1 by var2; var1 and var2 must be positive and var2 must be greater or equal
 to var1; the result is positive (leading bit equal to 0) and truncated to 16
 bits. If var1 = var2 then div(var1,var2) = 32767.

------------------------------------------------------------------------------
 REQUIREMENTS

 None

------------------------------------------------------------------------------
 REFERENCES

 [1] basicop2.c, ETS Version 2.0.0, February 8, 1999

------------------------------------------------------------------------------
 PSEUDO-CODE

Word16 div_s (Word16 var1, Word16 var2)
{
    Word16 var_out = 0;
    Word16 iteration;
    Word32 L_num;
    Word32 L_denom;
    Word16 abort_flag = 0;

    if ((var1 > var2) || (var1 < 0))
    {
        printf ("Division Error var1=%d  var2=%d\n", var1, var2);
        abort_flag = 1;
        exit(0);
    }
    if ((var1 != 0) && (abort_flag == 0))
    {
        if (var1 == var2)
        {
            var_out = MAX_16;
        }
        else
        {
            L_num = (Word32) var1;
            L_denom = (Word32) var2;

            for (iteration = 15; iteration > 0; iteration--)
            {
                var_out <<= 1;
                L_num <<= 1;

                if (L_num >= L_denom)
                {
                    L_num -= L_denom;
                    var_out += 1;
                }
            }
        }
    }

#if (WMOPS)
    multiCounter[currCounter].div_s++;
#endif
    return (var_out);
}

------------------------------------------------------------------------------
 RESOURCES USED
   When the code is written for a specific target processor the
     the resources used should be documented below.

 STACK USAGE: [stack count for this module] + [variable to represent
		  stack usage for each subroutine called]

     where: [stack usage variable] = stack usage for [subroutine
		 name] (see [filename].ext)

 DATA MEMORY USED: x words

 PROGRAM MEMORY USED: x words

 CLOCK CYCLES: [cycle count equation for this module] + [variable
		   used to represent cycle count for each subroutine
		   called]

     where: [cycle count variable] = cycle count for [subroutine
		name] (see [filename].ext)

------------------------------------------------------------------------------
*/


/*----------------------------------------------------------------------------
; 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
; Function Prototype declaration
----------------------------------------------------------------------------*/

/*----------------------------------------------------------------------------
; LOCAL STORE/BUFFER/POINTER DEFINITIONS
; Variable declaration - defined here and used outside this module
----------------------------------------------------------------------------*/

/*----------------------------------------------------------------------------
; EXTERNAL FUNCTION REFERENCES
; Declare functions defined elsewhere and referenced in this module
----------------------------------------------------------------------------*/

/*----------------------------------------------------------------------------
; EXTERNAL GLOBAL STORE/BUFFER/POINTER REFERENCES
; Declare variables used in this module but defined elsewhere
----------------------------------------------------------------------------*/

/*----------------------------------------------------------------------------
; FUNCTION CODE
----------------------------------------------------------------------------*/
Word16 div_s(register Word16 var1, register Word16 var2)
{
    /*----------------------------------------------------------------------------
    ; Define all local variables
    ----------------------------------------------------------------------------*/
    Word16 var_out = 0;
    register Word16 iteration;
    Word32 L_num;
    Word32 L_denom;
    Word32 L_denom_by_2;
    Word32 L_denom_by_4;

    /*----------------------------------------------------------------------------
    ; Function body here
    ----------------------------------------------------------------------------*/
    if ((var1 > var2) || (var1 < 0))
    {
        return 0; // used to exit(0);
    }
    if (var1)
    {
        if (var1 != var2)
        {

            L_num = (Word32) var1;
            L_denom = (Word32) var2;
            L_denom_by_2 = (L_denom << 1);
            L_denom_by_4 = (L_denom << 2);
            for (iteration = 5; iteration > 0; iteration--)
            {
                var_out <<= 3;
                L_num   <<= 3;

                if (L_num >= L_denom_by_4)
                {
                    L_num -= L_denom_by_4;
                    var_out |= 4;
                }

                if (L_num >= L_denom_by_2)
                {
                    L_num -= L_denom_by_2;
                    var_out |=  2;
                }

                if (L_num >= (L_denom))
                {
                    L_num -= (L_denom);
                    var_out |=  1;
                }

            }
        }
        else
        {
            var_out = MAX_16;
        }
    }

#if (WMOPS)
    multiCounter[currCounter].div_s++;
#endif

    /*----------------------------------------------------------------------------
    ; Return nothing or data or data pointer
    ----------------------------------------------------------------------------*/
    return (var_out);
}