/*
***********************************************************************
*
* Copyright (C) 1999 Ericsson Radio Systems AB
* 
* The Association of Radio Industries and Businesses (ARIB) has the
* licence to reproduce, distribute and publish the Bit Exact C Code
* programs in this CD-ROM together with the other parts of the RCR
* STD-27 (Personal Digital Cellular Telecommunication System)
* specification.
* 
* Ericsson has declared Option 1 (royalty-free licence) to ARIB for
* its Essential Industrial Property Rights related to the ACELP
* specification and the Bit Exact C Code programs. The royalty-free
* licence is limited to the development and manufacturing of
* products complying with the RCR STD-27H specification (or
* subsequent versions) for sale and use in Japan. Copying of the
* program(s) for any other purpose requires the prior written
* permission from Ericsson.
* 
* The user of the Bit Exact C Code hereby acknowledges the
* following:
* 
* 1.  Ericsson does not provide the user with any warranties,
*     whether express or implied, including but not limited to
*     warranties of merchantability and fitness for a particular
*     purpose relating to the Bit Exact C Code.
* 
* 2.  Ericsson shall have no responsibility whatsoever to indemnify
*     the user against actions or claims for infringement of any
*     intellectual property rights, e.g. patents, copyrights,
*     registered designs or any other rights, by reason of the
*     user's use of the Bit Exact C Code.
* 
***********************************************************************
*/

/*************************************************************************
 *
 *  FUNCTION: preemphasis()
 *
 *  PURPOSE: Preemphasis: filtering through 1 - g z^-1
 *
 *************************************************************************/

#include "typedef.h"
#include "basic_op.h"

void preemphasis(
    Word16 * signal, /* (i/o) : input signal overwritten by the output */
    Word16 g,        /* (i)   : preemphasis coefficient                */
    Word16 L         /* (i)   : size of filtering                      */
)
{
    static Word16 mem_pre = 0;
    Word16 *p1, *p2, temp, i;

    p1 = signal + L - 1;
    p2 = p1 - 1;
    temp = *p1;

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

    *p1 = sub(*p1, mult(g, mem_pre));

    mem_pre = temp;

    return;
}
