codec_g726.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 1999 - 2006, Digium, Inc.
 *
 * Mark Spencer <markster@digium.com>
 * Kevin P. Fleming <kpfleming@digium.com>
 *
 * Based on frompcm.c and topcm.c from the Emiliano MIPL browser/
 * interpreter.  See http://www.bsdtelephony.com.mx
 *
 * 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_g726.c - translate between signed linear and ITU G.726-32kbps (both RFC3551 and AAL2 codeword packing)
 *
 * \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 WANT_ASM
#include "log2comp.h"
 
/* define NOT_BLI to use a faster but not bit-level identical version */
/* #define NOT_BLI */
 
#if defined(NOT_BLI)
#   if defined(_MSC_VER)
typedef __int64 sint64;
#   elif defined(__GNUC__)
typedef long long sint64;
#   else
#       error 64-bit integer type is not defined for your compiler/platform
#   endif
#endif
 
#define BUFFER_SAMPLES   8096   /* size for the translation buffers */
#define BUF_SHIFT   5
 
/* Sample frame data */
#include "asterisk/slin.h"
#include "ex_g726.h"
 
/*
 * The following is the definition of the state structure
 * used by the G.726 encoder and decoder to preserve their internal
 * state between successive calls.  The meanings of the majority
 * of the state structure fields are explained in detail in the
 * CCITT Recommendation G.721.  The field names are essentially identical
 * to variable names in the bit level description of the coding algorithm
 * included in this Recommendation.
 */
struct g726_state {
    long yl;    /* Locked or steady state step size multiplier. */
    int yu;     /* Unlocked or non-steady state step size multiplier. */
    int dms;    /* Short term energy estimate. */
    int dml;    /* Long term energy estimate. */
    int ap;     /* Linear weighting coefficient of 'yl' and 'yu'. */
    int a[2];   /* Coefficients of pole portion of prediction filter.
             * stored as fixed-point 1==2^14 */
    int b[6];   /* Coefficients of zero portion of prediction filter.
             * stored as fixed-point 1==2^14 */
    int pk[2];  /* Signs of previous two samples of a partially
             * reconstructed signal. */
    int dq[6];      /* Previous 6 samples of the quantized difference signal
             * stored as fixed point 1==2^12,
             * or in internal floating point format */
    int sr[2];  /* Previous 2 samples of the quantized difference signal
             * stored as fixed point 1==2^12,
             * or in internal floating point format */
    int td;     /* delayed tone detect, new in 1988 version */
};
 
static int qtab_721[7] = {-124, 80, 178, 246, 300, 349, 400};
/*
 * Maps G.721 code word to reconstructed scale factor normalized log
 * magnitude values.
 */
static int _dqlntab[16] = {-2048, 4, 135, 213, 273, 323, 373, 425,
                425, 373, 323, 273, 213, 135, 4, -2048};
 
/* Maps G.721 code word to log of scale factor multiplier. */
static int _witab[16] = {-12, 18, 41, 64, 112, 198, 355, 1122,
                1122, 355, 198, 112, 64, 41, 18, -12};
/*
 * Maps G.721 code words to a set of values whose long and short
 * term averages are computed and then compared to give an indication
 * how stationary (steady state) the signal is.
 */
static int _fitab[16] = {0, 0, 0, 0x200, 0x200, 0x200, 0x600, 0xE00,
                0xE00, 0x600, 0x200, 0x200, 0x200, 0, 0, 0};
 
 
/*
 * g72x_init_state()
 *
 * This routine initializes and/or resets the g726_state structure
 * pointed to by 'state_ptr'.
 * All the initial state values are specified in the CCITT G.721 document.
 */
static void g726_init_state(struct g726_state *state_ptr)
{
    int     cnta;
 
    state_ptr->yl = 34816;
    state_ptr->yu = 544;
    state_ptr->dms = 0;
    state_ptr->dml = 0;
    state_ptr->ap = 0;
    for (cnta = 0; cnta < 2; cnta++) {
        state_ptr->a[cnta] = 0;
        state_ptr->pk[cnta] = 0;
#ifdef NOT_BLI
        state_ptr->sr[cnta] = 1;
#else
        state_ptr->sr[cnta] = 32;
#endif
    }
    for (cnta = 0; cnta < 6; cnta++) {
        state_ptr->b[cnta] = 0;
#ifdef NOT_BLI
        state_ptr->dq[cnta] = 1;
#else
        state_ptr->dq[cnta] = 32;
#endif
    }
    state_ptr->td = 0;
}
 
/*
 * quan()
 *
 * quantizes the input val against the table of integers.
 * It returns i if table[i - 1] <= val < table[i].
 *
 * Using linear search for simple coding.
 */
static int quan(int val, int *table, int size)
{
    int     i;
 
    for (i = 0; i < size && val >= *table; ++i, ++table)
        ;
    return i;
}
 
#ifdef NOT_BLI /* faster non-identical version */
 
/*
 * predictor_zero()
 *
 * computes the estimated signal from 6-zero predictor.
 *
 */
static int predictor_zero(struct g726_state *state_ptr)
{   /* divide by 2 is necessary here to handle negative numbers correctly */
    int i;
    sint64 sezi;
    for (sezi = 0, i = 0; i < 6; i++)           /* ACCUM */
        sezi += (sint64)state_ptr->b[i] * state_ptr->dq[i];
    return (int)(sezi >> 13) / 2 /* 2^14 */;
}
 
/*
 * predictor_pole()
 *
 * computes the estimated signal from 2-pole predictor.
 *
 */
static int predictor_pole(struct g726_state *state_ptr)
{   /* divide by 2 is necessary here to handle negative numbers correctly */
    return (int)(((sint64)state_ptr->a[1] * state_ptr->sr[1] +
                  (sint64)state_ptr->a[0] * state_ptr->sr[0]) >> 13) / 2 /* 2^14 */;
}
 
#else /* NOT_BLI - identical version */
/*
 * fmult()
 *
 * returns the integer product of the fixed-point number "an" (1==2^12) and
 * "floating point" representation (4-bit exponent, 6-bit mantessa) "srn".
 */
static int fmult(int an, int srn)
{
    int     anmag, anexp, anmant;
    int     wanexp, wanmant;
    int     retval;
 
    anmag = (an > 0) ? an : ((-an) & 0x1FFF);
    anexp = ilog2(anmag) - 5;
    anmant = (anmag == 0) ? 32 :
        (anexp >= 0) ? anmag >> anexp : anmag << -anexp;
    wanexp = anexp + ((srn >> 6) & 0xF) - 13;
 
    wanmant = (anmant * (srn & 077) + 0x30) >> 4;
    retval = (wanexp >= 0) ? ((wanmant << wanexp) & 0x7FFF) :
        (wanmant >> -wanexp);
 
    return (((an ^ srn) < 0) ? -retval : retval);
}
 
static int predictor_zero(struct g726_state *state_ptr)
{
    int     i;
    int     sezi;
    for (sezi = 0, i = 0; i < 6; i++)           /* ACCUM */
        sezi += fmult(state_ptr->b[i] >> 2, state_ptr->dq[i]);
    return sezi;
}
 
static int predictor_pole(struct g726_state *state_ptr)
{
    return (fmult(state_ptr->a[1] >> 2, state_ptr->sr[1]) +
            fmult(state_ptr->a[0] >> 2, state_ptr->sr[0]));
}
 
#endif /* NOT_BLI */
 
/*
 * step_size()
 *
 * computes the quantization step size of the adaptive quantizer.
 *
 */
static int step_size(struct g726_state *state_ptr)
{
    int y, dif, al;
 
    if (state_ptr->ap >= 256) {
        return state_ptr->yu;
    }
 
    y = state_ptr->yl >> 6;
    dif = state_ptr->yu - y;
    al = state_ptr->ap >> 2;
 
    if (dif > 0) {
        y += (dif * al) >> 6;
    } else if (dif < 0) {
        y += (dif * al + 0x3F) >> 6;
    }
    return y;
}
 
/*
 * quantize()
 *
 * Given a raw sample, 'd', of the difference signal and a
 * quantization step size scale factor, 'y', this routine returns the
 * ADPCM codeword to which that sample gets quantized.  The step
 * size scale factor division operation is done in the log base 2 domain
 * as a subtraction.
 */
static int quantize(
    int     d,  /* Raw difference signal sample */
    int     y,  /* Step size multiplier */
    int     *table, /* quantization table */
    int     size)   /* table size of integers */
{
    int     dqm;    /* Magnitude of 'd' */
    int     exp;    /* Integer part of base 2 log of 'd' */
    int     mant;   /* Fractional part of base 2 log */
    int     dl;     /* Log of magnitude of 'd' */
    int     dln;    /* Step size scale factor normalized log */
    int     i;
 
    /*
     * LOG
     *
     * Compute base 2 log of 'd', and store in 'dl'.
     */
    dqm = abs(d);
    exp = ilog2(dqm);
    if (exp < 0) {
        exp = 0;
    }
    mant = ((dqm << 7) >> exp) & 0x7F;  /* Fractional portion. */
    dl = (exp << 7) | mant;
 
    /*
     * SUBTB
     *
     * "Divide" by step size multiplier.
     */
    dln = dl - (y >> 2);
 
    /*
     * QUAN
     *
     * Obtain codeword i for 'd'.
     */
    i = quan(dln, table, size);
    if (d < 0) {            /* take 1's complement of i */
        return ((size << 1) + 1 - i);
    } else if (i == 0) {        /* take 1's complement of 0 */
        return ((size << 1) + 1); /* new in 1988 */
    } else {
        return i;
    }
}
 
/*
 * reconstruct()
 *
 * Returns reconstructed difference signal 'dq' obtained from
 * codeword 'i' and quantization step size scale factor 'y'.
 * Multiplication is performed in log base 2 domain as addition.
 */
static int reconstruct(
    int     sign,   /* 0 for non-negative value */
    int     dqln,   /* G.72x codeword */
    int     y)  /* Step size multiplier */
{
    int     dql;    /* Log of 'dq' magnitude */
    int     dex;    /* Integer part of log */
    int     dqt;
    int     dq; /* Reconstructed difference signal sample */
 
    dql = dqln + (y >> 2);  /* ADDA */
 
    if (dql < 0) {
#ifdef NOT_BLI
        return (sign) ? -1 : 1;
#else
        return (sign) ? -0x8000 : 0;
#endif
    } else {        /* ANTILOG */
        dex = (dql >> 7) & 15;
        dqt = 128 + (dql & 127);
#ifdef NOT_BLI
        dq = ((dqt << 19) >> (14 - dex));
        return (sign) ? -dq : dq;
#else
        dq = (dqt << 7) >> (14 - dex);
        return (sign) ? (dq - 0x8000) : dq;
#endif
    }
}
 
/*
 * update()
 *
 * updates the state variables for each output code
 */
static void update(
    int     code_size,  /* distinguish 723_40 with others */
    int     y,      /* quantizer step size */
    int     wi,     /* scale factor multiplier */
    int     fi,     /* for long/short term energies */
    int     dq,     /* quantized prediction difference */
    int     sr,     /* reconstructed signal */
    int     dqsez,      /* difference from 2-pole predictor */
    struct g726_state *state_ptr)   /* coder state pointer */
{
    int     cnt;
    int     mag;        /* Adaptive predictor, FLOAT A */
#ifndef NOT_BLI
    int     exp;
#endif
    int     a2p=0;      /* LIMC */
    int     a1ul;       /* UPA1 */
    int     pks1;       /* UPA2 */
    int     fa1;
    int     tr;         /* tone/transition detector */
    int     ylint, thr2, dqthr;
    int     ylfrac, thr1;
    int     pk0;
 
    pk0 = (dqsez < 0) ? 1 : 0;  /* needed in updating predictor poles */
 
#ifdef NOT_BLI
    mag = abs(dq / 0x1000); /* prediction difference magnitude */
#else
    mag = dq & 0x7FFF;      /* prediction difference magnitude */
#endif
    /* TRANS */
    ylint = state_ptr->yl >> 15;    /* exponent part of yl */
    ylfrac = (state_ptr->yl >> 10) & 0x1F;  /* fractional part of yl */
    thr1 = (32 + ylfrac) << ylint;      /* threshold */
    thr2 = (ylint > 9) ? 31 << 10 : thr1;   /* limit thr2 to 31 << 10 */
    dqthr = (thr2 + (thr2 >> 1)) >> 1;  /* dqthr = 0.75 * thr2 */
    if (state_ptr->td == 0) {       /* signal supposed voice */
        tr = 0;
    } else if (mag <= dqthr) {      /* supposed data, but small mag */
        tr = 0;         /* treated as voice */
    } else {                /* signal is data (modem) */
        tr = 1;
    }
    /*
     * Quantizer scale factor adaptation.
     */
 
    /* FUNCTW & FILTD & DELAY */
    /* update non-steady state step size multiplier */
    state_ptr->yu = y + ((wi - y) >> 5);
 
    /* LIMB */
    if (state_ptr->yu < 544) {  /* 544 <= yu <= 5120 */
        state_ptr->yu = 544;
    } else if (state_ptr->yu > 5120) {
        state_ptr->yu = 5120;
    }
 
    /* FILTE & DELAY */
    /* update steady state step size multiplier */
    state_ptr->yl += state_ptr->yu + ((-state_ptr->yl) >> 6);
 
    /*
     * Adaptive predictor coefficients.
     */
    if (tr == 1) {          /* reset a's and b's for modem signal */
        state_ptr->a[0] = 0;
        state_ptr->a[1] = 0;
        state_ptr->b[0] = 0;
        state_ptr->b[1] = 0;
        state_ptr->b[2] = 0;
        state_ptr->b[3] = 0;
        state_ptr->b[4] = 0;
        state_ptr->b[5] = 0;
    } else {            /* update a's and b's */
        pks1 = pk0 ^ state_ptr->pk[0];      /* UPA2 */
 
        /* update predictor pole a[1] */
        a2p = state_ptr->a[1] - (state_ptr->a[1] >> 7);
        if (dqsez != 0) {
            fa1 = (pks1) ? state_ptr->a[0] : -state_ptr->a[0];
            if (fa1 < -8191) {  /* a2p = function of fa1 */
                a2p -= 0x100;
            } else if (fa1 > 8191) {
                a2p += 0xFF;
            } else {
                a2p += fa1 >> 5;
            }
 
            if (pk0 ^ state_ptr->pk[1]) {
                /* LIMC */
                if (a2p <= -12160) {
                    a2p = -12288;
                } else if (a2p >= 12416) {
                    a2p = 12288;
                } else {
                    a2p -= 0x80;
                }
            } else if (a2p <= -12416) {
                a2p = -12288;
            } else if (a2p >= 12160) {
                a2p = 12288;
            } else {
                a2p += 0x80;
            }
        }
 
        /* TRIGB & DELAY */
        state_ptr->a[1] = a2p;
 
        /* UPA1 */
        /* update predictor pole a[0] */
        state_ptr->a[0] -= state_ptr->a[0] >> 8;
        if (dqsez != 0) {
            if (pks1 == 0)
                state_ptr->a[0] += 192;
            else
                state_ptr->a[0] -= 192;
        }
        /* LIMD */
        a1ul = 15360 - a2p;
        if (state_ptr->a[0] < -a1ul) {
            state_ptr->a[0] = -a1ul;
        } else if (state_ptr->a[0] > a1ul) {
            state_ptr->a[0] = a1ul;
        }
 
        /* UPB : update predictor zeros b[6] */
        for (cnt = 0; cnt < 6; cnt++) {
            if (code_size == 5) {       /* for 40Kbps G.723 */
                state_ptr->b[cnt] -= state_ptr->b[cnt] >> 9;
            } else {            /* for G.721 and 24Kbps G.723 */
                state_ptr->b[cnt] -= state_ptr->b[cnt] >> 8;
            }
            if (mag) {  /* XOR */
                if ((dq ^ state_ptr->dq[cnt]) >= 0) {
                    state_ptr->b[cnt] += 128;
                } else {
                    state_ptr->b[cnt] -= 128;
                }
            }
        }
    }
 
    for (cnt = 5; cnt > 0; cnt--)
        state_ptr->dq[cnt] = state_ptr->dq[cnt-1];
#ifdef NOT_BLI
    state_ptr->dq[0] = dq;
#else
    /* FLOAT A : convert dq[0] to 4-bit exp, 6-bit mantissa f.p. */
    if (mag == 0) {
        state_ptr->dq[0] = (dq >= 0) ? 0x20 : 0x20 - 0x400;
    } else {
        exp = ilog2(mag) + 1;
        state_ptr->dq[0] = (dq >= 0) ?
            (exp << 6) + ((mag << 6) >> exp) :
            (exp << 6) + ((mag << 6) >> exp) - 0x400;
    }
#endif
 
    state_ptr->sr[1] = state_ptr->sr[0];
#ifdef NOT_BLI
    state_ptr->sr[0] = sr;
#else
    /* FLOAT B : convert sr to 4-bit exp., 6-bit mantissa f.p. */
    if (sr == 0) {
        state_ptr->sr[0] = 0x20;
    } else if (sr > 0) {
        exp = ilog2(sr) + 1;
        state_ptr->sr[0] = (exp << 6) + ((sr << 6) >> exp);
    } else if (sr > -0x8000) {
        mag = -sr;
        exp = ilog2(mag) + 1;
        state_ptr->sr[0] =  (exp << 6) + ((mag << 6) >> exp) - 0x400;
    } else
        state_ptr->sr[0] = 0x20 - 0x400;
#endif
 
    /* DELAY A */
    state_ptr->pk[1] = state_ptr->pk[0];
    state_ptr->pk[0] = pk0;
 
    /* TONE */
    if (tr == 1) {      /* this sample has been treated as data */
        state_ptr->td = 0;  /* next one will be treated as voice */
    } else if (a2p < -11776) {  /* small sample-to-sample correlation */
        state_ptr->td = 1;  /* signal may be data */
    } else {                /* signal is voice */
        state_ptr->td = 0;
    }
 
    /*
     * Adaptation speed control.
     */
    state_ptr->dms += (fi - state_ptr->dms) >> 5;       /* FILTA */
    state_ptr->dml += (((fi << 2) - state_ptr->dml) >> 7);  /* FILTB */
 
    if (tr == 1) {
        state_ptr->ap = 256;
    } else if (y < 1536) {                  /* SUBTC */
        state_ptr->ap += (0x200 - state_ptr->ap) >> 4;
    } else if (state_ptr->td == 1) {
        state_ptr->ap += (0x200 - state_ptr->ap) >> 4;
    } else if (abs((state_ptr->dms << 2) - state_ptr->dml) >=
        (state_ptr->dml >> 3)) {
        state_ptr->ap += (0x200 - state_ptr->ap) >> 4;
    } else {
        state_ptr->ap += (-state_ptr->ap) >> 4;
    }
}
 
/*
 * g726_decode()
 *
 * Description:
 *
 * Decodes a 4-bit code of G.726-32 encoded data of i and
 * returns the resulting linear PCM, A-law or u-law value.
 * return -1 for unknown out_coding value.
 */
static int g726_decode(int  i, struct g726_state *state_ptr)
{
    int     sezi, sez, se;  /* ACCUM */
    int     y;          /* MIX */
    int     sr;         /* ADDB */
    int     dq;
    int     dqsez;
 
    i &= 0x0f;          /* mask to get proper bits */
#ifdef NOT_BLI
    sezi = predictor_zero(state_ptr);
    sez = sezi;
    se = sezi + predictor_pole(state_ptr);  /* estimated signal */
#else
    sezi = predictor_zero(state_ptr);
    sez = sezi >> 1;
    se = (sezi + predictor_pole(state_ptr)) >> 1;   /* estimated signal */
#endif
 
    y = step_size(state_ptr);   /* dynamic quantizer step size */
 
    dq = reconstruct(i & 8, _dqlntab[i], y); /* quantized diff. */
 
#ifdef NOT_BLI
    sr = se + dq;               /* reconst. signal */
    dqsez = dq + sez;           /* pole prediction diff. */
#else
    sr = (dq < 0) ? se - (dq & 0x3FFF) : se + dq;   /* reconst. signal */
    dqsez = sr - se + sez;      /* pole prediction diff. */
#endif
 
    update(4, y, _witab[i] << 5, _fitab[i], dq, sr, dqsez, state_ptr);
 
#ifdef NOT_BLI
    return (sr >> 10);  /* sr was 26-bit dynamic range */
#else
    return (sr << 2);   /* sr was 14-bit dynamic range */
#endif
}
 
/*
 * g726_encode()
 *
 * Encodes the input vale of linear PCM, A-law or u-law data sl and returns
 * the resulting code. -1 is returned for unknown input coding value.
 */
static int g726_encode(int sl, struct g726_state *state_ptr)
{
    int     sezi, se, sez;      /* ACCUM */
    int     d;          /* SUBTA */
    int     sr;         /* ADDB */
    int     y;          /* MIX */
    int     dqsez;          /* ADDC */
    int     dq, i;
 
#ifdef NOT_BLI
    sl <<= 10;          /* 26-bit dynamic range */
 
    sezi = predictor_zero(state_ptr);
    sez = sezi;
    se = sezi + predictor_pole(state_ptr);  /* estimated signal */
#else
    sl >>= 2;           /* 14-bit dynamic range */
 
    sezi = predictor_zero(state_ptr);
    sez = sezi >> 1;
    se = (sezi + predictor_pole(state_ptr)) >> 1;   /* estimated signal */
#endif
 
    d = sl - se;                /* estimation difference */
 
    /* quantize the prediction difference */
    y = step_size(state_ptr);       /* quantizer step size */
#ifdef NOT_BLI
    d /= 0x1000;
#endif
    i = quantize(d, y, qtab_721, 7);    /* i = G726 code */
 
    dq = reconstruct(i & 8, _dqlntab[i], y);    /* quantized est diff */
 
#ifdef NOT_BLI
    sr = se + dq;               /* reconst. signal */
    dqsez = dq + sez;           /* pole prediction diff. */
#else
    sr = (dq < 0) ? se - (dq & 0x3FFF) : se + dq;   /* reconst. signal */
    dqsez = sr - se + sez;          /* pole prediction diff. */
#endif
 
    update(4, y, _witab[i] << 5, _fitab[i], dq, sr, dqsez, state_ptr);
 
    return i;
}
 
/*
 * Private workspace for translating signed linear signals to G726.
 * Don't bother to define two distinct structs.
 */
 
struct g726_coder_pvt {
    /* buffer any odd byte in input - 0x80 + (value & 0xf) if present */
    unsigned char next_flag;
    struct g726_state g726;
};
 
/*! \brief init a new instance of g726_coder_pvt. */
static int lintog726_new(struct ast_trans_pvt *pvt)
{
    struct g726_coder_pvt *tmp = pvt->pvt;
 
    g726_init_state(&tmp->g726);
 
    return 0;
}
 
/*! \brief decode packed 4-bit G726 values (AAL2 packing) and store in buffer. */
static int g726aal2tolin_framein (struct ast_trans_pvt *pvt, struct ast_frame *f)
{
    struct g726_coder_pvt *tmp = pvt->pvt;
    unsigned char *src = f->data.ptr;
    int16_t *dst = pvt->outbuf.i16 + pvt->samples;
    unsigned int i;
 
    for (i = 0; i < f->datalen; i++) {
        *dst++ = g726_decode((src[i] >> 4) & 0xf, &tmp->g726);
        *dst++ = g726_decode(src[i] & 0x0f, &tmp->g726);
    }
 
    pvt->samples += f->samples;
    pvt->datalen += 2 * f->samples; /* 2 bytes/sample */
 
    return 0;
}
 
/*! \brief compress and store data (4-bit G726 samples, AAL2 packing) in outbuf */
static int lintog726aal2_framein(struct ast_trans_pvt *pvt, struct ast_frame *f)
{
    struct g726_coder_pvt *tmp = pvt->pvt;
    int16_t *src = f->data.ptr;
    unsigned int i;
 
    for (i = 0; i < f->samples; i++) {
        unsigned char d = g726_encode(src[i], &tmp->g726); /* this sample */
 
        if (tmp->next_flag & 0x80) {    /* merge with leftover sample */
            pvt->outbuf.c[pvt->datalen++] = ((tmp->next_flag & 0xf)<< 4) | d;
            pvt->samples += 2;  /* 2 samples per byte */
            tmp->next_flag = 0;
        } else {
            tmp->next_flag = 0x80 | d;
        }
    }
 
    return 0;
}
 
/*! \brief decode packed 4-bit G726 values (RFC3551 packing) and store in buffer. */
static int g726tolin_framein (struct ast_trans_pvt *pvt, struct ast_frame *f)
{
    struct g726_coder_pvt *tmp = pvt->pvt;
    unsigned char *src = f->data.ptr;
    int16_t *dst = pvt->outbuf.i16 + pvt->samples;
    unsigned int i;
 
    for (i = 0; i < f->datalen; i++) {
        *dst++ = g726_decode(src[i] & 0x0f, &tmp->g726);
        *dst++ = g726_decode((src[i] >> 4) & 0xf, &tmp->g726);
    }
 
    pvt->samples += f->samples;
    pvt->datalen += 2 * f->samples; /* 2 bytes/sample */
 
    return 0;
}
 
/*! \brief compress and store data (4-bit G726 samples, RFC3551 packing) in outbuf */
static int lintog726_framein(struct ast_trans_pvt *pvt, struct ast_frame *f)
{
    struct g726_coder_pvt *tmp = pvt->pvt;
    int16_t *src = f->data.ptr;
    unsigned int i;
 
    for (i = 0; i < f->samples; i++) {
        unsigned char d = g726_encode(src[i], &tmp->g726); /* this sample */
 
        if (tmp->next_flag & 0x80) {    /* merge with leftover sample */
            pvt->outbuf.c[pvt->datalen++] = (d << 4) | (tmp->next_flag & 0xf);
            pvt->samples += 2;  /* 2 samples per byte */
            tmp->next_flag = 0;
        } else {
            tmp->next_flag = 0x80 | d;
        }
    }
 
    return 0;
}
 
static struct ast_translator g726tolin = {
    .name = "g726tolin",
    .src_codec = {
        .name = "g726",
        .type = AST_MEDIA_TYPE_AUDIO,
        .sample_rate = 8000,
    },
    .dst_codec = {
        .name = "slin",
        .type = AST_MEDIA_TYPE_AUDIO,
        .sample_rate = 8000,
    },
    .format = "slin",
    .newpvt = lintog726_new,    /* same for both directions */
    .framein = g726tolin_framein,
    .sample = g726_sample,
    .desc_size = sizeof(struct g726_coder_pvt),
    .buffer_samples = BUFFER_SAMPLES,
    .buf_size = BUFFER_SAMPLES * 2,
};
 
static struct ast_translator lintog726 = {
    .name = "lintog726",
    .src_codec = {
        .name = "slin",
        .type = AST_MEDIA_TYPE_AUDIO,
        .sample_rate = 8000,
    },
    .dst_codec = {
        .name = "g726",
        .type = AST_MEDIA_TYPE_AUDIO,
        .sample_rate = 8000,
    },
    .format = "g726",
    .newpvt = lintog726_new,    /* same for both directions */
    .framein = lintog726_framein,
    .sample = slin8_sample,
    .desc_size = sizeof(struct g726_coder_pvt),
    .buffer_samples = BUFFER_SAMPLES,
    .buf_size = BUFFER_SAMPLES/2,
};
 
static struct ast_translator g726aal2tolin = {
    .name = "g726aal2tolin",
    .src_codec = {
        .name = "g726aal2",
        .type = AST_MEDIA_TYPE_AUDIO,
        .sample_rate = 8000,
    },
    .dst_codec = {
        .name = "slin",
        .type = AST_MEDIA_TYPE_AUDIO,
        .sample_rate = 8000,
    },
    .format = "slin",
    .newpvt = lintog726_new,    /* same for both directions */
    .framein = g726aal2tolin_framein,
    .sample = g726_sample,
    .desc_size = sizeof(struct g726_coder_pvt),
    .buffer_samples = BUFFER_SAMPLES,
    .buf_size = BUFFER_SAMPLES * 2,
};
 
static struct ast_translator lintog726aal2 = {
    .name = "lintog726aal2",
    .src_codec = {
        .name = "slin",
        .type = AST_MEDIA_TYPE_AUDIO,
        .sample_rate = 8000,
    },
    .dst_codec = {
        .name = "g726aal2",
        .type = AST_MEDIA_TYPE_AUDIO,
        .sample_rate = 8000,
    },
    .format = "g726aal2",
    .newpvt = lintog726_new,    /* same for both directions */
    .framein = lintog726aal2_framein,
    .sample = slin8_sample,
    .desc_size = sizeof(struct g726_coder_pvt),
    .buffer_samples = BUFFER_SAMPLES,
    .buf_size = BUFFER_SAMPLES / 2,
};
 
static int unload_module(void)
{
    int res = 0;
 
    res |= ast_unregister_translator(&g726tolin);
    res |= ast_unregister_translator(&lintog726);
 
    res |= ast_unregister_translator(&g726aal2tolin);
    res |= ast_unregister_translator(&lintog726aal2);
 
    return res;
}
 
static int load_module(void)
{
    int res = 0;
 
    res |= ast_register_translator(&g726tolin);
    res |= ast_register_translator(&lintog726);
 
    res |= ast_register_translator(&g726aal2tolin);
    res |= ast_register_translator(&lintog726aal2);
 
    if (res) {
        unload_module();
        return AST_MODULE_LOAD_DECLINE;
    }
 
    return AST_MODULE_LOAD_SUCCESS;
}
 
AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_DEFAULT, "ITU G.726-32kbps G726 Transcoder",
    .support_level = AST_MODULE_SUPPORT_CORE,
    .load = load_module,
    .unload = unload_module,
);