/*
********************************************************************************
*
*      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             : preemph.c
*      Purpose          : Preemphasis filtering
*      Description      : Filtering through 1 - g z^-1 
*
********************************************************************************
*/

/*
********************************************************************************
*                         MODULE INCLUDE FILE AND VERSION ID
********************************************************************************
*/
#include "namespace.h"
#include "preemph.h"

/*
********************************************************************************
*                         INCLUDE FILES
********************************************************************************
*/
#include "typedef.h"
#include "basic_op.h"
#include "no_count.h"

/*
********************************************************************************
*                         LOCAL VARIABLES AND TABLES
********************************************************************************
*/

/*
********************************************************************************
*                         PUBLIC PROGRAM CODE
********************************************************************************
*/

/*************************************************************************
*
*  Function:   preemphasis_reset
*  Purpose:    Initializes state memory to zero
*
**************************************************************************
*/
void preemphasis_reset (preemphasisState *state)
{
  state->mem_pre = 0;
}
 
/*
**************************************************************************
*  Function:  preemphasis
*  Purpose:   Filtering through 1 - g z^-1 
*
**************************************************************************
*/
int preemphasis (
    preemphasisState *st, /* (i/o)  : preemphasis filter state    */
    Word16 *signal, /* (i/o)   : input signal overwritten by the output */
    Word16 g,       /* (i)     : preemphasis coefficient                */
    Word16 L        /* (i)     : size of filtering                      */
)
{
    Word16 *p1, *p2, temp, i;

    p1 = signal + L - 1;                    move16 (); 
    p2 = p1 - 1;                            move16 (); 
    temp = *p1;                             move16 (); 

    for (i = 0; i <= L - 2; i++)
    {
        *p1 = sub (*p1, mult (g, *p2--));   move16 (); 
        p1--;
    }

    *p1 = sub (*p1, mult (g, st->mem_pre));     move16 (); 

    st->mem_pre = temp;                         move16 (); 

    return 0;
}