RTL271_1/amrnb/autocorr.c

/*
********************************************************************************
*
*      GSM AMR-NB speech codec   R98   Version 7.6.0   December 12, 2001
*                                R99   Version 3.3.0                
*                                REL-4 Version 4.1.0                
*
********************************************************************************
*
*      File             : autocorr.c
*
********************************************************************************
*/
/*
********************************************************************************
*                         MODULE INCLUDE FILE AND VERSION ID
********************************************************************************
*/
#include "autocorr.h"
const char autocorr_id[] = "@(#)$Id $" autocorr_h;
 
/*
********************************************************************************
*                         INCLUDE FILES
********************************************************************************
*/
#include "typedef.h"
#include "basic_op.h"
#include "oper_32b.h"
#include "count.h"
#include "cnst.h"

/*
********************************************************************************
*                         LOCAL VARIABLES AND TABLES
********************************************************************************
*/
 
/*
********************************************************************************
*                         PUBLIC PROGRAM CODE
********************************************************************************
*/
/*
**************************************************************************
*
*  Function    : autocorr
*  Purpose     : Compute autocorrelations of signal with windowing
*
**************************************************************************
*/
Word16 Autocorr (
    Word16 x[],            /* (i)    : Input signal (L_WINDOW)            */
    Word16 m,              /* (i)    : LPC order                          */
    Word16 r_h[],          /* (o)    : Autocorrelations  (msb)            */
    Word16 r_l[],          /* (o)    : Autocorrelations  (lsb)            */
    const Word16 wind[]    /* (i)    : window for LPC analysis (L_WINDOW) */
)
{
    Word16 i, j, norm;
    Word16 y[L_WINDOW];
    Word32 sum;
    Word16 overfl, overfl_shft;

    /* Windowing of signal */

    for (i = 0; i < L_WINDOW; i++)
    {
        y[i] = mult_r_ex (x[i], wind[i]); move16 (); 
    }

    /* Compute r[0] and test for overflow */

    overfl_shft = 0;                   move16 (); 

    do
    {
        overfl = 0;                    move16 (); 
        sum = 0L;                      move32 ();

        for (i = 0; i < L_WINDOW; i++)
        {
            sum = L_mac_ex (sum, y[i], y[i]);
        }

        /* If overflow divide y[] by 4 */

        test (); 
        if (L_sub_ex (sum, MAX_32) == 0L)
        {
            overfl_shft = add_ex (overfl_shft, 4);
            overfl = 1;                move16 (); /* Set the overflow flag */

            for (i = 0; i < L_WINDOW; i++)
            {
                y[i] = shr_ex (y[i], 2);  move16 (); 
            }
        }
        test (); 
    }
    while (overfl != 0);

    sum = L_add_ex (sum, 1L);             /* Avoid the case of all zeros */

    /* Normalization of r[0] */

    norm = norm_l_ex (sum);
    sum = L_shl_ex (sum, norm);
    L_Extract (sum, &r_h[0], &r_l[0]); /* Put in DPF format (see oper_32b) */

    /* r[1] to r[m] */

    for (i = 1; i <= m; i++)
    {
        sum = 0;                       move32 (); 

        for (j = 0; j < L_WINDOW - i; j++)
        {
            sum = L_mac_ex (sum, y[j], y[j + i]);
        }

        sum = L_shl_ex (sum, norm);
        L_Extract (sum, &r_h[i], &r_l[i]);
    }

    norm = sub_ex (norm, overfl_shft);

    return norm;
}