# isdn_audio.c

    /* $Id$

     * Linux ISDN subsystem, audio conversion and compression (linklevel).
     *
     * Copyright 1994,95,96 by Fritz Elfert (fritz@wuemaus.franken.de)
     * DTMF code (c) 1996 by Christian Mock (cm@kukuruz.ping.at)
     *
     * This program is free software; you can redistribute it and/or modify
     * it under the terms of the GNU General Public License as published by
     * the Free Software Foundation; either version 2, or (at your option)
     * any later version.
     *
     * This program is distributed in the hope that it will be useful,
     * but WITHOUT ANY WARRANTY; without even the implied warranty of
     * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     * GNU General Public License for more details.
     *
     * You should have received a copy of the GNU General Public License
     * along with this program; if not, write to the Free Software
     * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
     *
     * $Log$
     * Revision 1.11  1998/04/10 10:35:10  paul
     * fixed (silly?) warnings from egcs on Alpha.
     *
     * Revision 1.10  1998/02/20 17:09:40  fritz
     * Changes for recent kernels.
     *
     * Revision 1.9  1997/10/01 09:20:25  fritz
     * Removed old compatibility stuff for 2.0.X kernels.
     * From now on, this code is for 2.1.X ONLY!
     * Old stuff is still in the separate branch.
     *
     * Revision 1.8  1997/03/02 14:29:16  fritz
     * More ttyI related cleanup.
     *
     * Revision 1.7  1997/02/03 22:44:11  fritz
     * Reformatted according CodingStyle
     *
     * Revision 1.6  1996/06/06 14:43:31  fritz
     * Changed to support DTMF decoding on audio playback also.
     *
     * Revision 1.5  1996/06/05 02:24:08  fritz
     * Added DTMF decoder for audio mode.
     *
     * Revision 1.4  1996/05/17 03:48:01  fritz
     * Removed some test statements.
     * Added revision string.
     *
     * Revision 1.3  1996/05/10 08:48:11  fritz
     * Corrected adpcm bugs.
     *
     * Revision 1.2  1996/04/30 09:31:17  fritz
     * General rewrite.
     *
     * Revision 1.1.1.1  1996/04/28 12:25:40  fritz
     * Taken under CVS control
     *
     */

    #define __NO_VERSION__
    #include <linux/module.h>
    #include <linux/isdn.h>
    #include "isdn_audio.h"
    #include "isdn_common.h"

    char *isdn_audio_revision = "$Revision$";

    /*
     * Misc. lookup-tables.
     */

    /* ulaw -> signed 16-bit */
    static short isdn_audio_ulaw_to_s16[] =
    {
    	0x8284, 0x8684, 0x8a84, 0x8e84, 0x9284, 0x9684, 0x9a84, 0x9e84,
    	0xa284, 0xa684, 0xaa84, 0xae84, 0xb284, 0xb684, 0xba84, 0xbe84,
    	0xc184, 0xc384, 0xc584, 0xc784, 0xc984, 0xcb84, 0xcd84, 0xcf84,
    	0xd184, 0xd384, 0xd584, 0xd784, 0xd984, 0xdb84, 0xdd84, 0xdf84,
    	0xe104, 0xe204, 0xe304, 0xe404, 0xe504, 0xe604, 0xe704, 0xe804,
    	0xe904, 0xea04, 0xeb04, 0xec04, 0xed04, 0xee04, 0xef04, 0xf004,
    	0xf0c4, 0xf144, 0xf1c4, 0xf244, 0xf2c4, 0xf344, 0xf3c4, 0xf444,
    	0xf4c4, 0xf544, 0xf5c4, 0xf644, 0xf6c4, 0xf744, 0xf7c4, 0xf844,
    	0xf8a4, 0xf8e4, 0xf924, 0xf964, 0xf9a4, 0xf9e4, 0xfa24, 0xfa64,
    	0xfaa4, 0xfae4, 0xfb24, 0xfb64, 0xfba4, 0xfbe4, 0xfc24, 0xfc64,
    	0xfc94, 0xfcb4, 0xfcd4, 0xfcf4, 0xfd14, 0xfd34, 0xfd54, 0xfd74,
    	0xfd94, 0xfdb4, 0xfdd4, 0xfdf4, 0xfe14, 0xfe34, 0xfe54, 0xfe74,
    	0xfe8c, 0xfe9c, 0xfeac, 0xfebc, 0xfecc, 0xfedc, 0xfeec, 0xfefc,
    	0xff0c, 0xff1c, 0xff2c, 0xff3c, 0xff4c, 0xff5c, 0xff6c, 0xff7c,
    	0xff88, 0xff90, 0xff98, 0xffa0, 0xffa8, 0xffb0, 0xffb8, 0xffc0,
    	0xffc8, 0xffd0, 0xffd8, 0xffe0, 0xffe8, 0xfff0, 0xfff8, 0x0000,
    	0x7d7c, 0x797c, 0x757c, 0x717c, 0x6d7c, 0x697c, 0x657c, 0x617c,
    	0x5d7c, 0x597c, 0x557c, 0x517c, 0x4d7c, 0x497c, 0x457c, 0x417c,
    	0x3e7c, 0x3c7c, 0x3a7c, 0x387c, 0x367c, 0x347c, 0x327c, 0x307c,
    	0x2e7c, 0x2c7c, 0x2a7c, 0x287c, 0x267c, 0x247c, 0x227c, 0x207c,
    	0x1efc, 0x1dfc, 0x1cfc, 0x1bfc, 0x1afc, 0x19fc, 0x18fc, 0x17fc,
    	0x16fc, 0x15fc, 0x14fc, 0x13fc, 0x12fc, 0x11fc, 0x10fc, 0x0ffc,
    	0x0f3c, 0x0ebc, 0x0e3c, 0x0dbc, 0x0d3c, 0x0cbc, 0x0c3c, 0x0bbc,
    	0x0b3c, 0x0abc, 0x0a3c, 0x09bc, 0x093c, 0x08bc, 0x083c, 0x07bc,
    	0x075c, 0x071c, 0x06dc, 0x069c, 0x065c, 0x061c, 0x05dc, 0x059c,
    	0x055c, 0x051c, 0x04dc, 0x049c, 0x045c, 0x041c, 0x03dc, 0x039c,
    	0x036c, 0x034c, 0x032c, 0x030c, 0x02ec, 0x02cc, 0x02ac, 0x028c,
    	0x026c, 0x024c, 0x022c, 0x020c, 0x01ec, 0x01cc, 0x01ac, 0x018c,
    	0x0174, 0x0164, 0x0154, 0x0144, 0x0134, 0x0124, 0x0114, 0x0104,
    	0x00f4, 0x00e4, 0x00d4, 0x00c4, 0x00b4, 0x00a4, 0x0094, 0x0084,
    	0x0078, 0x0070, 0x0068, 0x0060, 0x0058, 0x0050, 0x0048, 0x0040,
    	0x0038, 0x0030, 0x0028, 0x0020, 0x0018, 0x0010, 0x0008, 0x0000
    };

    /* alaw -> signed 16-bit */
    static short isdn_audio_alaw_to_s16[] =
    {
    	0x13fc, 0xec04, 0x0144, 0xfebc, 0x517c, 0xae84, 0x051c, 0xfae4,
    	0x0a3c, 0xf5c4, 0x0048, 0xffb8, 0x287c, 0xd784, 0x028c, 0xfd74,
    	0x1bfc, 0xe404, 0x01cc, 0xfe34, 0x717c, 0x8e84, 0x071c, 0xf8e4,
    	0x0e3c, 0xf1c4, 0x00c4, 0xff3c, 0x387c, 0xc784, 0x039c, 0xfc64,
    	0x0ffc, 0xf004, 0x0104, 0xfefc, 0x417c, 0xbe84, 0x041c, 0xfbe4,
    	0x083c, 0xf7c4, 0x0008, 0xfff8, 0x207c, 0xdf84, 0x020c, 0xfdf4,
    	0x17fc, 0xe804, 0x018c, 0xfe74, 0x617c, 0x9e84, 0x061c, 0xf9e4,
    	0x0c3c, 0xf3c4, 0x0084, 0xff7c, 0x307c, 0xcf84, 0x030c, 0xfcf4,
    	0x15fc, 0xea04, 0x0164, 0xfe9c, 0x597c, 0xa684, 0x059c, 0xfa64,
    	0x0b3c, 0xf4c4, 0x0068, 0xff98, 0x2c7c, 0xd384, 0x02cc, 0xfd34,
    	0x1dfc, 0xe204, 0x01ec, 0xfe14, 0x797c, 0x8684, 0x07bc, 0xf844,
    	0x0f3c, 0xf0c4, 0x00e4, 0xff1c, 0x3c7c, 0xc384, 0x03dc, 0xfc24,
    	0x11fc, 0xee04, 0x0124, 0xfedc, 0x497c, 0xb684, 0x049c, 0xfb64,
    	0x093c, 0xf6c4, 0x0028, 0xffd8, 0x247c, 0xdb84, 0x024c, 0xfdb4,
    	0x19fc, 0xe604, 0x01ac, 0xfe54, 0x697c, 0x9684, 0x069c, 0xf964,
    	0x0d3c, 0xf2c4, 0x00a4, 0xff5c, 0x347c, 0xcb84, 0x034c, 0xfcb4,
    	0x12fc, 0xed04, 0x0134, 0xfecc, 0x4d7c, 0xb284, 0x04dc, 0xfb24,
    	0x09bc, 0xf644, 0x0038, 0xffc8, 0x267c, 0xd984, 0x026c, 0xfd94,
    	0x1afc, 0xe504, 0x01ac, 0xfe54, 0x6d7c, 0x9284, 0x06dc, 0xf924,
    	0x0dbc, 0xf244, 0x00b4, 0xff4c, 0x367c, 0xc984, 0x036c, 0xfc94,
    	0x0f3c, 0xf0c4, 0x00f4, 0xff0c, 0x3e7c, 0xc184, 0x03dc, 0xfc24,
    	0x07bc, 0xf844, 0x0008, 0xfff8, 0x1efc, 0xe104, 0x01ec, 0xfe14,
    	0x16fc, 0xe904, 0x0174, 0xfe8c, 0x5d7c, 0xa284, 0x05dc, 0xfa24,
    	0x0bbc, 0xf444, 0x0078, 0xff88, 0x2e7c, 0xd184, 0x02ec, 0xfd14,
    	0x14fc, 0xeb04, 0x0154, 0xfeac, 0x557c, 0xaa84, 0x055c, 0xfaa4,
    	0x0abc, 0xf544, 0x0058, 0xffa8, 0x2a7c, 0xd584, 0x02ac, 0xfd54,
    	0x1cfc, 0xe304, 0x01cc, 0xfe34, 0x757c, 0x8a84, 0x075c, 0xf8a4,
    	0x0ebc, 0xf144, 0x00d4, 0xff2c, 0x3a7c, 0xc584, 0x039c, 0xfc64,
    	0x10fc, 0xef04, 0x0114, 0xfeec, 0x457c, 0xba84, 0x045c, 0xfba4,
    	0x08bc, 0xf744, 0x0018, 0xffe8, 0x227c, 0xdd84, 0x022c, 0xfdd4,
    	0x18fc, 0xe704, 0x018c, 0xfe74, 0x657c, 0x9a84, 0x065c, 0xf9a4,
    	0x0cbc, 0xf344, 0x0094, 0xff6c, 0x327c, 0xcd84, 0x032c, 0xfcd4
    };

    /* alaw -> ulaw */
    static char isdn_audio_alaw_to_ulaw[] =
    {
    	0xab, 0x2b, 0xe3, 0x63, 0x8b, 0x0b, 0xc9, 0x49,
    	0xba, 0x3a, 0xf6, 0x76, 0x9b, 0x1b, 0xd7, 0x57,
    	0xa3, 0x23, 0xdd, 0x5d, 0x83, 0x03, 0xc1, 0x41,
    	0xb2, 0x32, 0xeb, 0x6b, 0x93, 0x13, 0xcf, 0x4f,
    	0xaf, 0x2f, 0xe7, 0x67, 0x8f, 0x0f, 0xcd, 0x4d,
    	0xbe, 0x3e, 0xfe, 0x7e, 0x9f, 0x1f, 0xdb, 0x5b,
    	0xa7, 0x27, 0xdf, 0x5f, 0x87, 0x07, 0xc5, 0x45,
    	0xb6, 0x36, 0xef, 0x6f, 0x97, 0x17, 0xd3, 0x53,
    	0xa9, 0x29, 0xe1, 0x61, 0x89, 0x09, 0xc7, 0x47,
    	0xb8, 0x38, 0xf2, 0x72, 0x99, 0x19, 0xd5, 0x55,
    	0xa1, 0x21, 0xdc, 0x5c, 0x81, 0x01, 0xbf, 0x3f,
    	0xb0, 0x30, 0xe9, 0x69, 0x91, 0x11, 0xce, 0x4e,
    	0xad, 0x2d, 0xe5, 0x65, 0x8d, 0x0d, 0xcb, 0x4b,
    	0xbc, 0x3c, 0xfa, 0x7a, 0x9d, 0x1d, 0xd9, 0x59,
    	0xa5, 0x25, 0xde, 0x5e, 0x85, 0x05, 0xc3, 0x43,
    	0xb4, 0x34, 0xed, 0x6d, 0x95, 0x15, 0xd1, 0x51,
    	0xac, 0x2c, 0xe4, 0x64, 0x8c, 0x0c, 0xca, 0x4a,
    	0xbb, 0x3b, 0xf8, 0x78, 0x9c, 0x1c, 0xd8, 0x58,
    	0xa4, 0x24, 0xde, 0x5e, 0x84, 0x04, 0xc2, 0x42,
    	0xb3, 0x33, 0xec, 0x6c, 0x94, 0x14, 0xd0, 0x50,
    	0xb0, 0x30, 0xe8, 0x68, 0x90, 0x10, 0xce, 0x4e,
    	0xbf, 0x3f, 0xfe, 0x7e, 0xa0, 0x20, 0xdc, 0x5c,
    	0xa8, 0x28, 0xe0, 0x60, 0x88, 0x08, 0xc6, 0x46,
    	0xb7, 0x37, 0xf0, 0x70, 0x98, 0x18, 0xd4, 0x54,
    	0xaa, 0x2a, 0xe2, 0x62, 0x8a, 0x0a, 0xc8, 0x48,
    	0xb9, 0x39, 0xf4, 0x74, 0x9a, 0x1a, 0xd6, 0x56,
    	0xa2, 0x22, 0xdd, 0x5d, 0x82, 0x02, 0xc0, 0x40,
    	0xb1, 0x31, 0xea, 0x6a, 0x92, 0x12, 0xcf, 0x4f,
    	0xae, 0x2e, 0xe6, 0x66, 0x8e, 0x0e, 0xcc, 0x4c,
    	0xbd, 0x3d, 0xfc, 0x7c, 0x9e, 0x1e, 0xda, 0x5a,
    	0xa6, 0x26, 0xdf, 0x5f, 0x86, 0x06, 0xc4, 0x44,
    	0xb5, 0x35, 0xee, 0x6e, 0x96, 0x16, 0xd2, 0x52
    };

    /* ulaw -> alaw */
    static char isdn_audio_ulaw_to_alaw[] =
    {
    	0xab, 0x55, 0xd5, 0x15, 0x95, 0x75, 0xf5, 0x35,
    	0xb5, 0x45, 0xc5, 0x05, 0x85, 0x65, 0xe5, 0x25,
    	0xa5, 0x5d, 0xdd, 0x1d, 0x9d, 0x7d, 0xfd, 0x3d,
    	0xbd, 0x4d, 0xcd, 0x0d, 0x8d, 0x6d, 0xed, 0x2d,
    	0xad, 0x51, 0xd1, 0x11, 0x91, 0x71, 0xf1, 0x31,
    	0xb1, 0x41, 0xc1, 0x01, 0x81, 0x61, 0xe1, 0x21,
    	0x59, 0xd9, 0x19, 0x99, 0x79, 0xf9, 0x39, 0xb9,
    	0x49, 0xc9, 0x09, 0x89, 0x69, 0xe9, 0x29, 0xa9,
    	0xd7, 0x17, 0x97, 0x77, 0xf7, 0x37, 0xb7, 0x47,
    	0xc7, 0x07, 0x87, 0x67, 0xe7, 0x27, 0xa7, 0xdf,
    	0x9f, 0x7f, 0xff, 0x3f, 0xbf, 0x4f, 0xcf, 0x0f,
    	0x8f, 0x6f, 0xef, 0x2f, 0x53, 0x13, 0x73, 0x33,
    	0xb3, 0x43, 0xc3, 0x03, 0x83, 0x63, 0xe3, 0x23,
    	0xa3, 0x5b, 0xdb, 0x1b, 0x9b, 0x7b, 0xfb, 0x3b,
    	0xbb, 0xbb, 0x4b, 0x4b, 0xcb, 0xcb, 0x0b, 0x0b,
    	0x8b, 0x8b, 0x6b, 0x6b, 0xeb, 0xeb, 0x2b, 0x2b,
    	0xab, 0x54, 0xd4, 0x14, 0x94, 0x74, 0xf4, 0x34,
    	0xb4, 0x44, 0xc4, 0x04, 0x84, 0x64, 0xe4, 0x24,
    	0xa4, 0x5c, 0xdc, 0x1c, 0x9c, 0x7c, 0xfc, 0x3c,
    	0xbc, 0x4c, 0xcc, 0x0c, 0x8c, 0x6c, 0xec, 0x2c,
    	0xac, 0x50, 0xd0, 0x10, 0x90, 0x70, 0xf0, 0x30,
    	0xb0, 0x40, 0xc0, 0x00, 0x80, 0x60, 0xe0, 0x20,
    	0x58, 0xd8, 0x18, 0x98, 0x78, 0xf8, 0x38, 0xb8,
    	0x48, 0xc8, 0x08, 0x88, 0x68, 0xe8, 0x28, 0xa8,
    	0xd6, 0x16, 0x96, 0x76, 0xf6, 0x36, 0xb6, 0x46,
    	0xc6, 0x06, 0x86, 0x66, 0xe6, 0x26, 0xa6, 0xde,
    	0x9e, 0x7e, 0xfe, 0x3e, 0xbe, 0x4e, 0xce, 0x0e,
    	0x8e, 0x6e, 0xee, 0x2e, 0x52, 0x12, 0x72, 0x32,
    	0xb2, 0x42, 0xc2, 0x02, 0x82, 0x62, 0xe2, 0x22,
    	0xa2, 0x5a, 0xda, 0x1a, 0x9a, 0x7a, 0xfa, 0x3a,
    	0xba, 0xba, 0x4a, 0x4a, 0xca, 0xca, 0x0a, 0x0a,
    	0x8a, 0x8a, 0x6a, 0x6a, 0xea, 0xea, 0x2a, 0x2a
    };

    #define NCOEFF           16     /* number of frequencies to be analyzed       */
    #define DTMF_TRESH    50000     /* above this is dtmf                         */
    #define SILENCE_TRESH   100     /* below this is silence                      */
    #define H2_TRESH      10000     /* 2nd harmonic                               */
    #define AMP_BITS          9     /* bits per sample, reduced to avoid overflow */
    #define LOGRP             0
    #define HIGRP             1

    typedef struct {
    	int grp;                /* low/high group     */
    	int k;                  /* k                  */
    	int k2;                 /* k fuer 2. harmonic */
    } dtmf_t;

    /* For DTMF recognition:
     * 2 * cos(2 * PI * k / N) precalculated for all k
     */
    static int cos2pik[NCOEFF] =
    {
    	55812, 29528, 53603, 24032, 51193, 14443, 48590, 6517,
    	38113, -21204, 33057, -32186, 25889, -45081, 18332, -55279
    };

    static dtmf_t dtmf_tones[8] =
    {
    	{LOGRP, 0, 1},          /*  697 Hz */
    	{LOGRP, 2, 3},          /*  770 Hz */
    	{LOGRP, 4, 5},          /*  852 Hz */
    	{LOGRP, 6, 7},          /*  941 Hz */
    	{HIGRP, 8, 9},          /* 1209 Hz */
    	{HIGRP, 10, 11},        /* 1336 Hz */
    	{HIGRP, 12, 13},        /* 1477 Hz */
    	{HIGRP, 14, 15}         /* 1633 Hz */
    };

    static char dtmf_matrix[4][4] =
    {
    	{'1', '2', '3', 'A'},
    	{'4', '5', '6', 'B'},
    	{'7', '8', '9', 'C'},
    	{'*', '0', '#', 'D'}
    };

    #if ((CPU == 386) || (CPU == 486) || (CPU == 586))
    static inline void
    isdn_audio_tlookup(const void *table, void *buff, unsigned long n)
    {
    	__asm__("cld\n"
    		"1:\tlodsb\n\t"
    		"xlatb\n\t"
    		"stosb\n\t"
    		"loop 1b\n\t"
          : :  "b"((long) table), "c"(n), "D"((long) buff), "S"((long) buff)
          :        "bx", "cx", "di", "si", "ax");
    }

    #else
    static inline void
    isdn_audio_tlookup(const char *table, char *buff, unsigned long n)
    {
    	while (n--)
    		*buff++ = table[*(unsigned char *)buff];
    }
    #endif

    void
    isdn_audio_ulaw2alaw(unsigned char *buff, unsigned long len)
    {
    	isdn_audio_tlookup(isdn_audio_ulaw_to_alaw, buff, len);
    }

    void
    isdn_audio_alaw2ulaw(unsigned char *buff, unsigned long len)
    {
    	isdn_audio_tlookup(isdn_audio_alaw_to_ulaw, buff, len);
    }

    /*
     * linear <-> adpcm conversion stuff
     * Most parts from the mgetty-package.
     * (C) by Gert Doering and Klaus Weidner
     * Used by permission of Gert Doering
     */

    #define ZEROTRAP                /* turn on the trap as per the MIL-STD */
    #undef ZEROTRAP
    #define BIAS 0x84               /* define the add-in bias for 16 bit samples */
    #define CLIP 32635

    static unsigned char
    isdn_audio_linear2ulaw(int sample)
    {
    	static int exp_lut[256] =
    	{
    		0, 0, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3,
    		4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
    		5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
    		5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
    		6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
    		6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
    		6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
    		6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
    		7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
    		7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
    		7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
    		7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
    		7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
    		7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
    		7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
    		7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7
    	};
    	int sign,
    	 exponent,
    	 mantissa;
    	unsigned char ulawbyte;

    	/* Get the sample into sign-magnitude. */
    	sign = (sample >> 8) & 0x80;	/* set aside the sign  */
    	if (sign != 0)
    		sample = -sample;	/* get magnitude       */
    	if (sample > CLIP)
    		sample = CLIP;  /* clip the magnitude  */

    	/* Convert from 16 bit linear to ulaw. */
    	sample = sample + BIAS;
    	exponent = exp_lut[(sample >> 7) & 0xFF];
    	mantissa = (sample >> (exponent + 3)) & 0x0F;
    	ulawbyte = ~(sign | (exponent << 4) | mantissa);
    #ifdef ZEROTRAP
    	/* optional CCITT trap */
    	if (ulawbyte == 0)
    		ulawbyte = 0x02;
    #endif
    	return (ulawbyte);
    }

    static int Mx[3][8] =
    {
    	{0x3800, 0x5600, 0, 0, 0, 0, 0, 0},
    	{0x399a, 0x3a9f, 0x4d14, 0x6607, 0, 0, 0, 0},
    	{0x3556, 0x3556, 0x399A, 0x3A9F, 0x4200, 0x4D14, 0x6607, 0x6607},
    };

    static int bitmask[9] =
    {
    	0, 0x01, 0x03, 0x07, 0x0f, 0x1f, 0x3f, 0x7f, 0xff
    };

    static int
    isdn_audio_get_bits(adpcm_state * s, unsigned char **in, int *len)
    {
    	while (s->nleft < s->nbits) {
    		int d = *((*in)++);
    		(*len)--;
    		s->word = (s->word << 8) | d;
    		s->nleft += 8;
    	}
    	s->nleft -= s->nbits;
    	return (s->word >> s->nleft) & bitmask[s->nbits];
    }

    static void
    isdn_audio_put_bits(int data, int nbits, adpcm_state * s,
    		    unsigned char **out, int *len)
    {
    	s->word = (s->word << nbits) | (data & bitmask[nbits]);
    	s->nleft += nbits;
    	while (s->nleft >= 8) {
    		int d = (s->word >> (s->nleft - 8));
    		*(out[0]++) = d & 255;
    		(*len)++;
    		s->nleft -= 8;
    	}
    }

    adpcm_state *
    isdn_audio_adpcm_init(adpcm_state * s, int nbits)
    {
    	if (!s)
    		s = (adpcm_state *) kmalloc(sizeof(adpcm_state), GFP_ATOMIC);
    	if (s) {
    		s->a = 0;
    		s->d = 5;
    		s->word = 0;
    		s->nleft = 0;
    		s->nbits = nbits;
    	}
    	return s;
    }

    dtmf_state *
    isdn_audio_dtmf_init(dtmf_state * s)
    {
    	if (!s)
    		s = (dtmf_state *) kmalloc(sizeof(dtmf_state), GFP_ATOMIC);
    	if (s) {
    		s->idx = 0;
    		s->last = ' ';
    	}
    	return s;
    }

    /*
     * Decompression of adpcm data to a/u-law
     *
     */

    int
    isdn_audio_adpcm2xlaw(adpcm_state * s, int fmt, unsigned char *in,
    		      unsigned char *out, int len)
    {
    	int a = s->a;
    	int d = s->d;
    	int nbits = s->nbits;
    	int olen = 0;

    	while (len) {
    		int e = isdn_audio_get_bits(s, &in, &len);
    		int sign;

    		if (nbits == 4 && e == 0)
    			d = 4;
    		sign = (e >> (nbits - 1)) ? -1 : 1;
    		e &= bitmask[nbits - 1];
    		a += sign * ((e << 1) + 1) * d >> 1;
    		if (d & 1)
    			a++;
    		if (fmt)
    			*out++ = isdn_audio_ulaw_to_alaw[
    					 isdn_audio_linear2ulaw(a << 2)];
    		else
    			*out++ = isdn_audio_linear2ulaw(a << 2);
    		olen++;
    		d = (d * Mx[nbits - 2][e] + 0x2000) >> 14;
    		if (d < 5)
    			d = 5;
    	}
    	s->a = a;
    	s->d = d;
    	return olen;
    }

    int
    isdn_audio_2adpcm_flush(adpcm_state * s, unsigned char *out)
    {
    	int olen = 0;

    	if (s->nleft)
    		isdn_audio_put_bits(0, 8 - s->nleft, s, &out, &olen);
    	return olen;
    }

    int
    isdn_audio_xlaw2adpcm(adpcm_state * s, int fmt, unsigned char *in,
    		      unsigned char *out, int len)
    {
    	int a = s->a;
    	int d = s->d;
    	int nbits = s->nbits;
    	int olen = 0;

    	while (len--) {
    		int e = 0,
    		 nmax = 1 << (nbits - 1);
    		int sign,
    		 delta;

    		if (fmt)
    			delta = (isdn_audio_alaw_to_s16[*in++] >> 2) - a;
    		else
    			delta = (isdn_audio_ulaw_to_s16[*in++] >> 2) - a;
    		if (delta < 0) {
    			e = nmax;
    			delta = -delta;
    		}
    		while (--nmax && delta > d) {
    			delta -= d;
    			e++;
    		}
    		if (nbits == 4 && ((e & 0x0f) == 0))
    			e = 8;
    		isdn_audio_put_bits(e, nbits, s, &out, &olen);
    		sign = (e >> (nbits - 1)) ? -1 : 1;
    		e &= bitmask[nbits - 1];

    		a += sign * ((e << 1) + 1) * d >> 1;
    		if (d & 1)
    			a++;
    		d = (d * Mx[nbits - 2][e] + 0x2000) >> 14;
    		if (d < 5)
    			d = 5;
    	}
    	s->a = a;
    	s->d = d;
    	return olen;
    }

    /*
     * Goertzel algorithm.
     * See http://ptolemy.eecs.berkeley.edu/~pino/Ptolemy/papers/96/dtmf_ict/
     * for more info.
     * Result is stored into an sk_buff and queued up for later
     * evaluation.
     */
    static void
    isdn_audio_goertzel(int *sample, modem_info * info)
    {
    	int sk,
    	 sk1,
    	 sk2;
    	int k,
    	 n;
    	struct sk_buff *skb;
    	int *result;

    	skb = dev_alloc_skb(sizeof(int) * NCOEFF);
    	if (!skb) {
    		printk(KERN_WARNING
    		  "isdn_audio: Could not alloc DTMF result for ttyI%d\n",
    		       info->line);
    		return;
    	}
    	result = (int *) skb_put(skb, sizeof(int) * NCOEFF);
    	for (k = 0; k < NCOEFF; k++) {
    		sk = sk1 = sk2 = 0;
    		for (n = 0; n < DTMF_NPOINTS; n++) {
    			sk = sample[n] + ((cos2pik[k] * sk1) >> 15) - sk2;
    			sk2 = sk1;
    			sk1 = sk;
    		}
    		result[k] =
    		    ((sk * sk) >> AMP_BITS) -
    		    ((((cos2pik[k] * sk) >> 15) * sk2) >> AMP_BITS) +
    		    ((sk2 * sk2) >> AMP_BITS);
    	}
    	skb_queue_tail(&info->dtmf_queue, skb);
    	isdn_timer_ctrl(ISDN_TIMER_MODEMREAD, 1);
    }

    void
    isdn_audio_eval_dtmf(modem_info * info)
    {
    	struct sk_buff *skb;
    	int *result;
    	dtmf_state *s;
    	int silence;
    	int i;
    	int di;
    	int ch;
    	unsigned long flags;
    	int grp[2];
    	char what;
    	char *p;

    	while ((skb = skb_dequeue(&info->dtmf_queue))) {
    		result = (int *) skb->data;
    		s = info->dtmf_state;
    		grp[LOGRP] = grp[HIGRP] = -2;
    		silence = 0;
    		for (i = 0; i < 8; i++) {
    			if ((result[dtmf_tones[i].k] > DTMF_TRESH) &&
    			    (result[dtmf_tones[i].k2] < H2_TRESH))
    				grp[dtmf_tones[i].grp] = (grp[dtmf_tones[i].grp] == -2) ? i : -1;
    			else if ((result[dtmf_tones[i].k] < SILENCE_TRESH) &&
    			      (result[dtmf_tones[i].k2] < SILENCE_TRESH))
    				silence++;
    		}
    		if (silence == 8)
    			what = ' ';
    		else {
    			if ((grp[LOGRP] >= 0) && (grp[HIGRP] >= 0)) {
    				what = dtmf_matrix[grp[LOGRP]][grp[HIGRP] - 4];
    				if (s->last != ' ' && s->last != '.')
    					s->last = what;	/* min. 1 non-DTMF between DTMF */
    			} else
    				what = '.';
    		}
    		if ((what != s->last) && (what != ' ') && (what != '.')) {
    			printk(KERN_DEBUG "dtmf: tt='%c'\n", what);
    			p = skb->data;
    			*p++ = 0x10;
    			*p = what;
    			skb_trim(skb, 2);
    			if (skb_headroom(skb) < sizeof(isdn_audio_skb)) {
    				printk(KERN_WARNING
    				       "isdn_audio: insufficient skb_headroom, dropping\n");
    				kfree_skb(skb);
    				return;
    			}
    			ISDN_AUDIO_SKB_DLECOUNT(skb) = 0;
    			ISDN_AUDIO_SKB_LOCK(skb) = 0;
    			save_flags(flags);
    			cli();
    			di = info->isdn_driver;
    			ch = info->isdn_channel;
    			__skb_queue_tail(&dev->drv[di]->rpqueue[ch], skb);
    			dev->drv[di]->rcvcount[ch] += 2;
    			restore_flags(flags);
    			/* Schedule dequeuing */
    			if ((dev->modempoll) && (info->rcvsched))
    				isdn_timer_ctrl(ISDN_TIMER_MODEMREAD, 1);
    			wake_up_interruptible(&dev->drv[di]->rcv_waitq[ch]);
    		} else
    			kfree_skb(skb);
    		s->last = what;
    	}
    }

    /*
     * Decode DTMF tones, queue result in separate sk_buf for
     * later examination.
     * Parameters:
     *   s    = pointer to state-struct.
     *   buf  = input audio data
     *   len  = size of audio data.
     *   fmt  = audio data format (0 = ulaw, 1 = alaw)
     */
    void
    isdn_audio_calc_dtmf(modem_info * info, unsigned char *buf, int len, int fmt)
    {
    	dtmf_state *s = info->dtmf_state;
    	int i;
    	int c;

    	while (len) {
    		c = MIN(len, (DTMF_NPOINTS - s->idx));
    		if (c <= 0)
    			break;
    		for (i = 0; i < c; i++) {
    			if (fmt)
    				s->buf[s->idx++] =
    				    isdn_audio_alaw_to_s16[*buf++] >> (15 - AMP_BITS);
    			else
    				s->buf[s->idx++] =
    				    isdn_audio_ulaw_to_s16[*buf++] >> (15 - AMP_BITS);
    		}
    		if (s->idx == DTMF_NPOINTS) {
    			isdn_audio_goertzel(s->buf, info);
    			s->idx = 0;
    		}
    		len -= c;
    	}
    }