lsfwt.cpp

实现3GPP的GSM中AMR语音的CODECS。

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 * 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: ./audio/gsm-amr/c/src/lsfwt.c
 Functions: Lsf_wt

     Date: 02/01/2002

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

 Description: Updated to accept new parameter, Flag *pOverflow.  Placed
 file in the proper PV Software template.

 Description:
              1. Eliminated unused include files.
              2. Replaced array addressing by pointers
              3. Eliminated math operations that unnecessary checked for
                 saturation, by evaluating the operands
              4. Unrolled loops to speed up processing, use decrement loops

 Description:  Replaced "int" and/or "char" with OSCL defined types.

 Description:

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

 Inputs:
    lsf -- Pointer to Word16 -- LSF vector

 Outputs:
    wf -- Pointer to Word16 -- square of weighting factors
    pOverflow -- Pointer to type Flag -- Flag set when overflow occurs

 Returns:
    None

 Global Variables Used:
    None

 Local Variables Needed:
    None

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

Compute LSF weighting factors

 d[i] = lsf[i+1] - lsf[i-1]

 The weighting factors are approximated by two line segment

 First segment passes by the following 2 points:

    d[i] = 0Hz     wf[i] = 3.347
    d[i] = 450Hz   wf[i] = 1.8

 Second segment passes by the following 2 points:

    d[i] = 450Hz   wf[i] = 1.8
    d[i] = 1500Hz  wf[i] = 1.0

 if( d[i] < 450Hz )
   wf[i] = 3.347 - ( (3.347-1.8) / (450-0)) *  d[i]
 else
   wf[i] = 1.8 - ( (1.8-1.0) / (1500-450)) *  (d[i] - 450)


 if( d[i] < 1843)
   wf[i] = 3427 - (28160*d[i])>>15
 else
   wf[i] = 1843 - (6242*(d[i]-1843))>>15

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



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

 lsfwt.c, UMTS GSM AMR speech codec, R99 - Version 3.2.0, March 2, 2001

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



------------------------------------------------------------------------------
 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 "lsfwt.h"
#include "cnst.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
----------------------------------------------------------------------------*/

void Lsf_wt(
    Word16 *lsf,         /* input : LSF vector                  */
    Word16 *wf,          /* output: square of weighting factors */
    Flag   *pOverflow
)
{
    Word16 temp;
    Word16 wgt_fct;
    Word16 i;
    Word16 *p_wf = wf;
    Word16 *p_lsf   = &lsf[0];
    Word16 *p_lsf_2 = &lsf[1];

    OSCL_UNUSED_ARG(pOverflow);

    /* wf[0] = lsf[1] - 0  */
    *(p_wf++) = *(p_lsf_2++);

    for (i = 4; i != 0 ; i--)
    {
        *(p_wf++) = *(p_lsf_2++) - *(p_lsf++);
        *(p_wf++) = *(p_lsf_2++) - *(p_lsf++);
    }
    /*
     *  wf[9] = 4000 - lsf[8]
     */
    *(p_wf) = 16384 - *(p_lsf);

    p_wf = wf;

    for (i = 10; i != 0; i--)
    {
        /*
         *  (wf[i] - 450);
         *  1843 == 450 Hz (Q15 considering 7FFF = 8000 Hz)
         */
        wgt_fct = *p_wf;
        temp =  wgt_fct - 1843;

        if (temp > 0)
        {
            temp = (Word16)(((Word32)temp * 6242) >> 15);
            wgt_fct = 1843 - temp;
        }
        else
        {
            temp = (Word16)(((Word32)wgt_fct * 28160) >> 15);
            wgt_fct = 3427 - temp;
        }

        *(p_wf++) = wgt_fct << 3;

    } /* for (i = 10; i != 0; i--) */

    return;

} /* Lsf_wt() */