FFmpeg/libavcodec/g726.c

/*
 * G.726 ADPCM audio codec
 * Copyright (c) 2004 Roman Shaposhnik.
 *
 * This is a very straightforward rendition of the G.726
 * Section 4 "Computational Details".
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */
#include <limits.h>
#include "avcodec.h"
#include "common.h"
#include "bitstream.h"

/**
 * G.726 11bit float.
 * G.726 Standard uses rather odd 11bit floating point arithmentic for
 * numerous occasions. It's a mistery to me why they did it this way
 * instead of simply using 32bit integer arithmetic.
 */
typedef struct Float11 {
        int sign;   /**< 1bit sign */
        int exp;    /**< 4bit exponent */
        int mant;   /**< 6bit mantissa */
} Float11;

static inline Float11* i2f(int16_t i, Float11* f)
{
        f->sign = (i < 0);
        if (f->sign)
                i = -i;
        f->exp = av_log2_16bit(i) + !!i;
        f->mant = i? (i<<6) >> f->exp :
                         1<<5;
        return f;
}

static inline int16_t mult(Float11* f1, Float11* f2)
{
        int res, exp;

        exp = f1->exp + f2->exp;
        res = (((f1->mant * f2->mant) + 0x30) >> 4) << 7;
        res = exp > 26 ? res << (exp - 26) : res >> (26 - exp);
        return (f1->sign ^ f2->sign) ? -res : res;
}

static inline int sgn(int value)
{
   return (value < 0) ? -1 : 1;
}

typedef struct G726Tables {
        int  bits;            /**< bits per sample */
        int* quant;           /**< quantization table */
        int* iquant;          /**< inverse quantization table */
        int* W;               /**< special table #1 ;-) */
        int* F;               /**< special table #2 */
} G726Tables;

typedef struct G726Context {
         G726Tables* tbls;    /**< static tables needed for computation */

         Float11 sr[2];       /**< prev. reconstructed samples */
         Float11 dq[6];       /**< prev. difference */
         int a[2];            /**< second order predictor coeffs */
         int b[6];            /**< sixth order predictor coeffs */
         int pk[2];           /**< signs of prev. 2 sez + dq */

         int ap;              /**< scale factor control */
         int yu;              /**< fast scale factor */
         int yl;              /**< slow scale factor */
         int dms;             /**< short average magnitude of F[i] */
         int dml;             /**< long average magnitude of F[i] */
         int td;              /**< tone detect */

         int se;              /**< estimated signal for the next iteration */
         int sez;             /**< estimated second order prediction */
         int y;               /**< quantizer scaling factor for the next iteration */
} G726Context;

static int quant_tbl16[] =                       /**< 16kbit/s 2bits per sample */
           { 260, INT_MAX };
static int iquant_tbl16[] =
           { 116, 365, 365, 116 };
static int W_tbl16[] =
           { -22, 439, 439, -22 };
static int F_tbl16[] =
           { 0, 7, 7, 0 };

static int quant_tbl24[] =                       /**< 24kbit/s 3bits per sample */
           {  7, 217, 330, INT_MAX };
static int iquant_tbl24[] =
           { INT_MIN, 135, 273, 373, 373, 273, 135, INT_MIN };
static int W_tbl24[] =
           { -4,  30, 137, 582, 582, 137,  30, -4 };
static int F_tbl24[] =
           { 0, 1, 2, 7, 7, 2, 1, 0 };

static int quant_tbl32[] =                       /**< 32kbit/s 4bits per sample */
           { -125,  79, 177, 245, 299, 348, 399, INT_MAX };
static int iquant_tbl32[] =
           { INT_MIN,   4, 135, 213, 273, 323, 373, 425,
                 425, 373, 323, 273, 213, 135,   4, INT_MIN };
static int W_tbl32[] =
           { -12,  18,  41,  64, 112, 198, 355, 1122,
            1122, 355, 198, 112,  64,  41,  18, -12};
static int F_tbl32[] =
           { 0, 0, 0, 1, 1, 1, 3, 7, 7, 3, 1, 1, 1, 0, 0, 0 };

static int quant_tbl40[] =                      /**< 40kbit/s 5bits per sample */
           { -122, -16,  67, 138, 197, 249, 297, 338,
              377, 412, 444, 474, 501, 527, 552, INT_MAX };
static int iquant_tbl40[] =
           { INT_MIN, -66,  28, 104, 169, 224, 274, 318,
                 358, 395, 429, 459, 488, 514, 539, 566,
                 566, 539, 514, 488, 459, 429, 395, 358,
                 318, 274, 224, 169, 104,  28, -66, INT_MIN };
static int W_tbl40[] =
           {   14,  14,  24,  39,  40,  41,   58,  100,
              141, 179, 219, 280, 358, 440,  529,  696,
              696, 529, 440, 358, 280, 219,  179,  141,
              100,  58,  41,  40,  39,  24,   14,   14 };
static int F_tbl40[] =
           { 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 2, 3, 4, 5, 6, 6,
             6, 6, 5, 4, 3, 2, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0 };

static G726Tables G726Tables_pool[] =
           {{ 2, quant_tbl16, iquant_tbl16, W_tbl16, F_tbl16 },
            { 3, quant_tbl24, iquant_tbl24, W_tbl24, F_tbl24 },
            { 4, quant_tbl32, iquant_tbl32, W_tbl32, F_tbl32 },
            { 5, quant_tbl40, iquant_tbl40, W_tbl40, F_tbl40 }};


/**
 * Para 4.2.2 page 18: Adaptive quantizer.
 */
static inline uint8_t quant(G726Context* c, int d)
{
   int sign, exp, i, dln;

   sign = i = 0;
   if (d < 0) {
       sign = 1;
       d = -d;
   }
   exp = av_log2_16bit(d);
   dln = ((exp<<7) + (((d<<7)>>exp)&0x7f)) - (c->y>>2);

   while (c->tbls->quant[i] < INT_MAX && c->tbls->quant[i] < dln)
        ++i;

   if (sign)
       i = ~i;
   if (c->tbls->bits != 2 && i == 0) /* I'm not sure this is a good idea */
       i = 0xff;

   return i;
}

/**
 * Para 4.2.3 page 22: Inverse adaptive quantizer.
 */
static inline int16_t inverse_quant(G726Context* c, int i)
{
    int dql, dex, dqt;

    dql = c->tbls->iquant[i] + (c->y >> 2);
    dex = (dql>>7) & 0xf;        /* 4bit exponent */
    dqt = (1<<7) + (dql & 0x7f); /* log2 -> linear */
    return (dql < 0) ? 0 : ((dqt<<7) >> (14-dex));
}

static inline int16_t g726_iterate(G726Context* c, int16_t I)
{
    int dq, re_signal, pk0, fa1, i, tr, ylint, ylfrac, thr2, al, dq0;
    Float11 f;

    dq = inverse_quant(c, I);
    if (I >> (c->tbls->bits - 1))  /* get the sign */
        dq = -dq;
    re_signal = c->se + dq;

    /* Transition detect */
    ylint = (c->yl >> 15);
    ylfrac = (c->yl >> 10) & 0x1f;
    thr2 = (ylint > 9) ? 0x1f << 10 : (0x20 + ylfrac) << ylint;
    if (c->td == 1 && abs(dq) > ((thr2+(thr2>>1))>>1))
        tr = 1;
    else
        tr = 0;

    /* Update second order predictor coefficient A2 and A1 */
    pk0 = (c->sez + dq) ? sgn(c->sez + dq) : 0;
    dq0 = dq ? sgn(dq) : 0;
    if (tr) {
        c->a[0] = 0;
        c->a[1] = 0;
        for (i=0; i<6; i++)
           c->b[i] = 0;
    } else {
        /* This is a bit crazy, but it really is +255 not +256 */
        fa1 = clip((-c->a[0]*c->pk[0]*pk0)>>5, -256, 255);

        c->a[1] += 128*pk0*c->pk[1] + fa1 - (c->a[1]>>7);
        c->a[1] = clip(c->a[1], -12288, 12288);
        c->a[0] += 64*3*pk0*c->pk[0] - (c->a[0] >> 8);
        c->a[0] = clip(c->a[0], -(15360 - c->a[1]), 15360 - c->a[1]);

        for (i=0; i<6; i++)
             c->b[i] += 128*dq0*sgn(-c->dq[i].sign) - (c->b[i]>>8);
    }

    /* Update Dq and Sr and Pk */
    c->pk[1] = c->pk[0];
    c->pk[0] = pk0 ? pk0 : 1;
    c->sr[1] = c->sr[0];
    i2f(re_signal, &c->sr[0]);
    for (i=5; i>0; i--)
       c->dq[i] = c->dq[i-1];
    i2f(dq, &c->dq[0]);
    c->dq[0].sign = I >> (c->tbls->bits - 1); /* Isn't it crazy ?!?! */

    /* Update tone detect [I'm not sure 'tr == 0' is really needed] */
    c->td = (tr == 0 && c->a[1] < -11776);

    /* Update Ap */
    c->dms += ((c->tbls->F[I]<<9) - c->dms) >> 5;
    c->dml += ((c->tbls->F[I]<<11) - c->dml) >> 7;
    if (tr)
       c->ap = 256;
    else if (c->y > 1535 && !c->td && (abs((c->dms << 2) - c->dml) < (c->dml >> 3)))
       c->ap += (-c->ap) >> 4;
    else
       c->ap += (0x200 - c->ap) >> 4;

    /* Update Yu and Yl */
    c->yu = clip(c->y + (((c->tbls->W[I] << 5) - c->y) >> 5), 544, 5120);
    c->yl += c->yu + ((-c->yl)>>6);

    /* Next iteration for Y */
    al = (c->ap >= 256) ? 1<<6 : c->ap >> 2;
    c->y = (c->yl + (c->yu - (c->yl>>6))*al) >> 6;

    /* Next iteration for SE and SEZ */
    c->se = 0;
    for (i=0; i<6; i++)
       c->se += mult(i2f(c->b[i] >> 2, &f), &c->dq[i]);
    c->sez = c->se >> 1;
    for (i=0; i<2; i++)
       c->se += mult(i2f(c->a[i] >> 2, &f), &c->sr[i]);
    c->se >>= 1;

    return clip(re_signal << 2, -0xffff, 0xffff);
}

static int g726_reset(G726Context* c, int bit_rate)
{
    int i;

    c->tbls = &G726Tables_pool[bit_rate/8000 - 2];
    for (i=0; i<2; i++) {
       i2f(0, &c->sr[i]);
       c->a[i] = 0;
       c->pk[i] = 1;
    }
    for (i=0; i<6; i++) {
       i2f(0, &c->dq[i]);
       c->b[i] = 0;
    }
    c->ap = 0;
    c->dms = 0;
    c->dml = 0;
    c->yu = 544;
    c->yl = 34816;
    c->td = 0;

    c->se = 0;
    c->sez = 0;
    c->y = 544;

    return 0;
}

static int16_t g726_decode(G726Context* c, int16_t i)
{
    return g726_iterate(c, i);
}

#ifdef CONFIG_ENCODERS
static int16_t g726_encode(G726Context* c, int16_t sig)
{
   uint8_t i;

   i = quant(c, sig/4 - c->se) & ((1<<c->tbls->bits) - 1);
   g726_iterate(c, i);
   return i;
}
#endif

/* Interfacing to the libavcodec */

typedef struct AVG726Context {
   G726Context c;
   int bits_left;
   int bit_buffer;
   int code_size;
} AVG726Context;

static int g726_init(AVCodecContext * avctx)
{
    AVG726Context* c = (AVG726Context*)avctx->priv_data;

    if (avctx->channels != 1 ||
        (avctx->bit_rate != 16000 && avctx->bit_rate != 24000 &&
         avctx->bit_rate != 32000 && avctx->bit_rate != 40000)) {
        av_log(avctx, AV_LOG_ERROR, "G726: unsupported audio format\n");
        return -1;
    }
    if (avctx->sample_rate != 8000 && avctx->strict_std_compliance>FF_COMPLIANCE_INOFFICIAL) {
        av_log(avctx, AV_LOG_ERROR, "G726: unsupported audio format\n");
        return -1;
    }
    g726_reset(&c->c, avctx->bit_rate);
    c->code_size = c->c.tbls->bits;
    c->bit_buffer = 0;
    c->bits_left = 0;

    avctx->coded_frame = avcodec_alloc_frame();
    if (!avctx->coded_frame)
        return -ENOMEM;
    avctx->coded_frame->key_frame = 1;

    return 0;
}

static int g726_close(AVCodecContext *avctx)
{
    av_freep(&avctx->coded_frame);
    return 0;
}

#ifdef CONFIG_ENCODERS
static int g726_encode_frame(AVCodecContext *avctx,
                            uint8_t *dst, int buf_size, void *data)
{
    AVG726Context *c = avctx->priv_data;
    short *samples = data;
    PutBitContext pb;

    init_put_bits(&pb, dst, 1024*1024);

    for (; buf_size; buf_size--)
       put_bits(&pb, c->code_size, g726_encode(&c->c, *samples++));

    flush_put_bits(&pb);

    return put_bits_count(&pb)>>3;
}
#endif

static int g726_decode_frame(AVCodecContext *avctx,
                             void *data, int *data_size,
                             uint8_t *buf, int buf_size)
{
    AVG726Context *c = avctx->priv_data;
    short *samples = data;
    uint8_t code;
    uint8_t mask;
    GetBitContext gb;

    if (!buf_size)
        goto out;

    mask = (1<<c->code_size) - 1;
    init_get_bits(&gb, buf, buf_size * 8);
    if (c->bits_left) {
        int s = c->code_size - c->bits_left;;
        code = (c->bit_buffer << s) | get_bits(&gb, s);
        *samples++ = g726_decode(&c->c, code & mask);
    }

    while (get_bits_count(&gb) + c->code_size <= buf_size*8)
        *samples++ = g726_decode(&c->c, get_bits(&gb, c->code_size) & mask);

    c->bits_left = buf_size*8 - get_bits_count(&gb);
    c->bit_buffer = get_bits(&gb, c->bits_left);

out:
    *data_size = (uint8_t*)samples - (uint8_t*)data;
    return buf_size;
}

#ifdef CONFIG_ENCODERS
AVCodec adpcm_g726_encoder = {
    "g726",
    CODEC_TYPE_AUDIO,
    CODEC_ID_ADPCM_G726,
    sizeof(AVG726Context),
    g726_init,
    g726_encode_frame,
    g726_close,
    NULL,
};
#endif //CONFIG_ENCODERS

AVCodec adpcm_g726_decoder = {
    "g726",
    CODEC_TYPE_AUDIO,
    CODEC_ID_ADPCM_G726,
    sizeof(AVG726Context),
    g726_init,
    NULL,
    g726_close,
    g726_decode_frame,
};