l_extract.cpp

实现3GPP的GSM中AMR语音的CODECS。

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/****************************************************************************************
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/l_extract.c

     Date: 09/07/2000

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

 Description: Updated template. Changed function interface to pass in a
              pointer to overflow flag into the function instead of using a
              global flag. Changed names of function parameters for clarity.
              Removed inclusion of unwanted header files.

 Description:

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

/*----------------------------------------------------------------------------
; 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: L_extract
------------------------------------------------------------------------------
 INPUT AND OUTPUT DEFINITIONS

 Inputs:
	L_var = 32 bit signed integer (Word32) whose value falls
	       in the range : 0x8000 0000 <= L_32 <= 0x7fff ffff.

    pL_var_hi =  pointer to the most significant word of L_var (Word16).

    pL_var_lo =  pointer to the least significant word of L_var shifted
              to the left by 1 (Word16).

    pOverflow = pointer to overflow (Flag)

 Outputs:
    pOverflow -> 1 if the 32 bit add operation resulted in overflow
	pL_var_hi -> MS word of L_32.
	pL_var_lo -> LS word of L_32 shifted left by 1.

 Returns:
    None

 Global Variables Used:
    None

 Local Variables Needed:
    None

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

 This function extracts two 16-bit double precision format (DPF) numbers
 from a 32-bit integer. The MS word of L_var will be stored in the location
 pointed to by pL_var_hi and the shifted LS word of L_var will be stored in
 the location pointed to by pL_var_lo.

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

 None

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

 [1] L_extract() function in oper_32b.c,  UMTS GSM AMR speech codec, R99 -
 Version 3.2.0, March 2, 2001

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


------------------------------------------------------------------------------
 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
----------------------------------------------------------------------------*/
void L_Extract(Word32 L_var,
               Word16 *pL_var_hi,
               Word16 *pL_var_lo,
               Flag   *pOverflow)
{

    Word32  temp;

    OSCL_UNUSED_ARG(pOverflow);

    temp = (L_var >> 16);

    *(pL_var_hi) = (Word16) temp;
    *(pL_var_lo) = (Word16)((L_var >> 1) - (temp << 15));

    return;
}