codec_adpcm.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Based on frompcm.c and topcm.c from the Emiliano MIPL browser/
 * interpreter.  See http://www.bsdtelephony.com.mx
 *
 * Copyright (c) 2001 - 2005 Digium, Inc.
 * All rights reserved.
 *
 * Karl Sackett <krs@linux-support.net>, 2001-03-21
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */
 
/*! \file
 *
 * \brief codec_adpcm.c - translate between signed linear and Dialogic ADPCM
 *
 * \ingroup codecs
 */
 
/*** MODULEINFO
    <support_level>core</support_level>
 ***/
 
#include "asterisk.h"
 
#include "asterisk/lock.h"
#include "asterisk/linkedlists.h"
#include "asterisk/module.h"
#include "asterisk/config.h"
#include "asterisk/translate.h"
#include "asterisk/utils.h"
 
/* define NOT_BLI to use a faster but not bit-level identical version */
/* #define NOT_BLI */
 
#define BUFFER_SAMPLES   8096   /* size for the translation buffers */
 
/* Sample frame data */
#include "asterisk/slin.h"
#include "ex_adpcm.h"
 
/*
 * Step size index shift table
 */
 
static int indsft[8] = { -1, -1, -1, -1, 2, 4, 6, 8 };
 
/*
 * Step size table, where stpsz[i]=floor[16*(11/10)^i]
 */
 
static int stpsz[49] = {
  16, 17, 19, 21, 23, 25, 28, 31, 34, 37, 41, 45, 50, 55, 60, 66, 73,
  80, 88, 97, 107, 118, 130, 143, 157, 173, 190, 209, 230, 253, 279,
  307, 337, 371, 408, 449, 494, 544, 598, 658, 724, 796, 876, 963,
  1060, 1166, 1282, 1411, 1552
};
 
/*
 * Decoder/Encoder state
 *   States for both encoder and decoder are synchronized
 */
struct adpcm_state {
    int ssindex;
    int signal;
    int zero_count;
    int next_flag;
};
 
/*
 * Decode(encoded)
 *  Decodes the encoded nibble from the adpcm file.
 *
 * Results:
 *  Returns the encoded difference.
 *
 * Side effects:
 *  Sets the index to the step size table for the next encode.
 */
 
static inline short decode(int encoded, struct adpcm_state *state)
{
    int diff;
    int step;
    int sign;
 
    step = stpsz[state->ssindex];
 
    sign = encoded & 0x08;
    encoded &= 0x07;
#ifdef NOT_BLI
    diff = (((encoded << 1) + 1) * step) >> 3;
#else /* BLI code */
    diff = step >> 3;
    if (encoded & 4)
        diff += step;
    if (encoded & 2)
        diff += step >> 1;
    if (encoded & 1)
        diff += step >> 2;
    if ((encoded >> 1) & step & 0x1)
        diff++;
#endif
    if (sign)
        diff = -diff;
 
    if (state->next_flag & 0x1)
        state->signal -= 8;
    else if (state->next_flag & 0x2)
        state->signal += 8;
 
    state->signal += diff;
 
    if (state->signal > 2047)
        state->signal = 2047;
    else if (state->signal < -2047)
        state->signal = -2047;
 
    state->next_flag = 0;
 
#ifdef AUTO_RETURN
    if (encoded)
        state->zero_count = 0;
    else if (++(state->zero_count) == 24) {
        state->zero_count = 0;
        if (state->signal > 0)
            state->next_flag = 0x1;
        else if (state->signal < 0)
            state->next_flag = 0x2;
    }
#endif
 
    state->ssindex += indsft[encoded];
    if (state->ssindex < 0)
        state->ssindex = 0;
    else if (state->ssindex > 48)
        state->ssindex = 48;
 
    return state->signal << 4;
}
 
/*
 * Adpcm
 *  Takes a signed linear signal and encodes it as ADPCM
 *  For more information see http://en.wikipedia.org/wiki/Dialogic_ADPCM
 *
 * Results:
 *  Foo.
 *
 * Side effects:
 *  signal gets updated with each pass.
 */
 
static inline int adpcm(short csig, struct adpcm_state *state)
{
    int diff;
    int step;
    int encoded;
 
    /*
     * Clip csig if too large or too small
     */
    csig >>= 4;
 
    step = stpsz[state->ssindex];
    diff = csig - state->signal;
 
#ifdef NOT_BLI
    if (diff < 0) {
        encoded = (-diff << 2) / step;
        if (encoded > 7)
            encoded = 7;
        encoded |= 0x08;
    } else {
        encoded = (diff << 2) / step;
        if (encoded > 7)
            encoded = 7;
    }
#else /* BLI code */
    if (diff < 0) {
        encoded = 8;
        diff = -diff;
    } else
        encoded = 0;
    if (diff >= step) {
        encoded |= 4;
        diff -= step;
    }
    step >>= 1;
    if (diff >= step) {
        encoded |= 2;
        diff -= step;
    }
    step >>= 1;
    if (diff >= step)
        encoded |= 1;
#endif /* NOT_BLI */
 
    /* feedback to state */
    decode(encoded, state);
 
    return encoded;
}
 
/*----------------- Asterisk-codec glue ------------*/
 
/*! \brief Workspace for translating signed linear signals to ADPCM. */
struct adpcm_encoder_pvt {
    struct adpcm_state state;
    int16_t inbuf[BUFFER_SAMPLES];  /* Unencoded signed linear values */
};
 
/*! \brief Workspace for translating ADPCM signals to signed linear. */
struct adpcm_decoder_pvt {
    struct adpcm_state state;
};
 
/*! \brief decode 4-bit adpcm frame data and store in output buffer */
static int adpcmtolin_framein(struct ast_trans_pvt *pvt, struct ast_frame *f)
{
    struct adpcm_decoder_pvt *tmp = pvt->pvt;
    int x = f->datalen;
    unsigned char *src = f->data.ptr;
    int16_t *dst = pvt->outbuf.i16 + pvt->samples;
 
    while (x--) {
        *dst++ = decode((*src >> 4) & 0xf, &tmp->state);
        *dst++ = decode(*src++ & 0x0f, &tmp->state);
    }
    pvt->samples += f->samples;
    pvt->datalen += 2*f->samples;
    return 0;
}
 
/*! \brief fill input buffer with 16-bit signed linear PCM values. */
static int lintoadpcm_framein(struct ast_trans_pvt *pvt, struct ast_frame *f)
{
    struct adpcm_encoder_pvt *tmp = pvt->pvt;
 
    memcpy(&tmp->inbuf[pvt->samples], f->data.ptr, f->datalen);
    pvt->samples += f->samples;
    return 0;
}
 
/*! \brief convert inbuf and store into frame */
static struct ast_frame *lintoadpcm_frameout(struct ast_trans_pvt *pvt)
{
    struct adpcm_encoder_pvt *tmp = pvt->pvt;
    struct ast_frame *f;
    int i;
    int samples = pvt->samples; /* save original number */
 
    if (samples < 2)
        return NULL;
 
    pvt->samples &= ~1; /* atomic size is 2 samples */
 
    for (i = 0; i < pvt->samples; i += 2) {
        pvt->outbuf.c[i/2] =
            (adpcm(tmp->inbuf[i  ], &tmp->state) << 4) |
            (adpcm(tmp->inbuf[i+1], &tmp->state)     );
    };
 
    f = ast_trans_frameout(pvt, pvt->samples/2, 0);
 
    /*
     * If there is a left over sample, move it to the beginning
     * of the input buffer.
     */
 
    if (samples & 1) {  /* move the leftover sample at beginning */
        tmp->inbuf[0] = tmp->inbuf[samples - 1];
        pvt->samples = 1;
    }
    return f;
}
 
 
static struct ast_translator adpcmtolin = {
    .name = "adpcmtolin",
    .src_codec = {
        .name = "adpcm",
        .type = AST_MEDIA_TYPE_AUDIO,
        .sample_rate = 8000,
    },
    .dst_codec = {
        .name = "slin",
        .type = AST_MEDIA_TYPE_AUDIO,
        .sample_rate = 8000,
    },
    .format = "slin",
    .framein = adpcmtolin_framein,
    .sample = adpcm_sample,
    .desc_size = sizeof(struct adpcm_decoder_pvt),
    .buffer_samples = BUFFER_SAMPLES,
    .buf_size = BUFFER_SAMPLES * 2,
};
 
static struct ast_translator lintoadpcm = {
    .name = "lintoadpcm",
    .src_codec = {
        .name = "slin",
        .type = AST_MEDIA_TYPE_AUDIO,
        .sample_rate = 8000,
    },
    .dst_codec = {
        .name = "adpcm",
        .type = AST_MEDIA_TYPE_AUDIO,
        .sample_rate = 8000,
    },
    .format = "adpcm",
    .framein = lintoadpcm_framein,
    .frameout = lintoadpcm_frameout,
    .sample = slin8_sample,
    .desc_size = sizeof (struct adpcm_encoder_pvt),
    .buffer_samples = BUFFER_SAMPLES,
    .buf_size = BUFFER_SAMPLES/ 2,  /* 2 samples per byte */
};
 
static int unload_module(void)
{
    int res;
 
    res = ast_unregister_translator(&lintoadpcm);
    res |= ast_unregister_translator(&adpcmtolin);
 
    return res;
}
 
static int load_module(void)
{
    int res = 0;
 
    res = ast_register_translator(&adpcmtolin);
    res |= ast_register_translator(&lintoadpcm);
 
    if (res) {
        unload_module();
        return AST_MODULE_LOAD_DECLINE;
    }
 
    return AST_MODULE_LOAD_SUCCESS;
}
 
AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_DEFAULT, "Adaptive Differential PCM Coder/Decoder",
    .support_level = AST_MODULE_SUPPORT_CORE,
    .load = load_module,
    .unload = unload_module,
);