/*
** Copyright (c) 2002-2021, Erik de Castro Lopo <erikd@mega-nerd.com>
** All rights reserved.
**
** This code is released under 2-clause BSD license. Please see the
** file at : https://github.com/libsndfile/libsamplerate/blob/master/COPYING
*/

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

#include "common.h"

#define SINC_MAGIC_MARKER   MAKE_MAGIC (' ', 's', 'i', 'n', 'c', ' ')

/*========================================================================================
*/

#define MAKE_INCREMENT_T(x)     ((increment_t) (x))

#define SHIFT_BITS              12
#define FP_ONE                  ((double) (((increment_t) 1) << SHIFT_BITS))
#define INV_FP_ONE              (1.0 / FP_ONE)

/* Customixe max channls from Kconfig. */
#ifndef CONFIG_CHAN_NR
#define MAX_CHANNELS            128
#else
#define MAX_CHANNELS            CONFIG_CHAN_NR
#endif

/*========================================================================================
*/

typedef int32_t increment_t ;
typedef float   coeff_t ;
typedef int _CHECK_SHIFT_BITS[2 * (SHIFT_BITS < sizeof (increment_t) * 8 - 1) - 1]; /* sanity check. */

#ifdef ENABLE_SINC_FAST_CONVERTER
  #include "fastest_coeffs.h"
#endif
#ifdef ENABLE_SINC_MEDIUM_CONVERTER
  #include "mid_qual_coeffs.h"
#endif
#ifdef ENABLE_SINC_BEST_CONVERTER
  #include "high_qual_coeffs.h"
#endif

typedef struct
{   int     sinc_magic_marker ;

    long    in_count, in_used ;
    long    out_count, out_gen ;

    int     coeff_half_len, index_inc ;

    double  src_ratio, input_index ;

    coeff_t const   *coeffs ;

    int     b_current, b_end, b_real_end, b_len ;

    /* Sure hope noone does more than 128 channels at once. */
    double left_calc [MAX_CHANNELS], right_calc [MAX_CHANNELS] ;

    float   *buffer ;
} SINC_FILTER ;

static SRC_ERROR sinc_multichan_vari_process (SRC_STATE *state, SRC_DATA *data) ;
static SRC_ERROR sinc_hex_vari_process (SRC_STATE *state, SRC_DATA *data) ;
static SRC_ERROR sinc_quad_vari_process (SRC_STATE *state, SRC_DATA *data) ;
static SRC_ERROR sinc_stereo_vari_process (SRC_STATE *state, SRC_DATA *data) ;
static SRC_ERROR sinc_mono_vari_process (SRC_STATE *state, SRC_DATA *data) ;

static SRC_ERROR prepare_data (SINC_FILTER *filter, int channels, SRC_DATA *data, int half_filter_chan_len) WARN_UNUSED ;

static void sinc_reset (SRC_STATE *state) ;
static SRC_STATE *sinc_copy (SRC_STATE *state) ;
static void sinc_close (SRC_STATE *state) ;

static SRC_STATE_VT sinc_multichan_state_vt =
{
    sinc_multichan_vari_process,
    sinc_multichan_vari_process,
    sinc_reset,
    sinc_copy,
    sinc_close
} ;

static SRC_STATE_VT sinc_hex_state_vt =
{
    sinc_hex_vari_process,
    sinc_hex_vari_process,
    sinc_reset,
    sinc_copy,
    sinc_close
} ;

static SRC_STATE_VT sinc_quad_state_vt =
{
    sinc_quad_vari_process,
    sinc_quad_vari_process,
    sinc_reset,
    sinc_copy,
    sinc_close
} ;

static SRC_STATE_VT sinc_stereo_state_vt =
{
    sinc_stereo_vari_process,
    sinc_stereo_vari_process,
    sinc_reset,
    sinc_copy,
    sinc_close
} ;

static SRC_STATE_VT sinc_mono_state_vt =
{
    sinc_mono_vari_process,
    sinc_mono_vari_process,
    sinc_reset,
    sinc_copy,
    sinc_close
} ;

static inline increment_t
double_to_fp (double x)
{   return (increment_t) (psf_lrint ((x) * FP_ONE)) ;
} /* double_to_fp */

static inline increment_t
int_to_fp (int x)
{   return (((increment_t) (x)) << SHIFT_BITS) ;
} /* int_to_fp */

static inline int
fp_to_int (increment_t x)
{   return (((x) >> SHIFT_BITS)) ;
} /* fp_to_int */

static inline increment_t
fp_fraction_part (increment_t x)
{   return ((x) & ((((increment_t) 1) << SHIFT_BITS) - 1)) ;
} /* fp_fraction_part */

static inline double
fp_to_double (increment_t x)
{   return fp_fraction_part (x) * INV_FP_ONE ;
} /* fp_to_double */

static inline int
int_div_ceil (int divident, int divisor) /* == (int) ceil ((float) divident / divisor) */
{   assert (divident >= 0 && divisor > 0) ; /* For positive numbers only */
    return (divident + (divisor - 1)) / divisor ;
}

/*----------------------------------------------------------------------------------------
*/

LIBSAMPLERATE_DLL_PRIVATE const char*
sinc_get_name (int src_enum)
{
    switch (src_enum)
    {   case SRC_SINC_BEST_QUALITY :
            return "Best Sinc Interpolator" ;

        case SRC_SINC_MEDIUM_QUALITY :
            return "Medium Sinc Interpolator" ;

        case SRC_SINC_FASTEST :
            return "Fastest Sinc Interpolator" ;

        default: break ;
        } ;

    return NULL ;
} /* sinc_get_descrition */

LIBSAMPLERATE_DLL_PRIVATE const char*
sinc_get_description (int src_enum)
{
    switch (src_enum)
    {   case SRC_SINC_FASTEST :
            return "Band limited sinc interpolation, fastest, 97dB SNR, 80% BW." ;

        case SRC_SINC_MEDIUM_QUALITY :
            return "Band limited sinc interpolation, medium quality, 121dB SNR, 90% BW." ;

        case SRC_SINC_BEST_QUALITY :
            return "Band limited sinc interpolation, best quality, 144dB SNR, 96% BW." ;

        default :
            break ;
        } ;

    return NULL ;
} /* sinc_get_descrition */

static SINC_FILTER *
sinc_filter_new (int converter_type, int channels)
{
    assert (converter_type == SRC_SINC_FASTEST ||
        converter_type == SRC_SINC_MEDIUM_QUALITY ||
        converter_type == SRC_SINC_BEST_QUALITY) ;
    assert (channels > 0 && channels <= MAX_CHANNELS) ;

    SINC_FILTER *priv = (SINC_FILTER *) calloc (1, sizeof (SINC_FILTER)) ;
    if (priv)
    {
        priv->sinc_magic_marker = SINC_MAGIC_MARKER ;
        switch (converter_type)
        {
#ifdef ENABLE_SINC_FAST_CONVERTER
        case SRC_SINC_FASTEST :
            priv->coeffs = fastest_coeffs.coeffs ;
            priv->coeff_half_len = ARRAY_LEN (fastest_coeffs.coeffs) - 2 ;
            priv->index_inc = fastest_coeffs.increment ;
            break ;
#endif
#ifdef ENABLE_SINC_MEDIUM_CONVERTER
        case SRC_SINC_MEDIUM_QUALITY :
            priv->coeffs = slow_mid_qual_coeffs.coeffs ;
            priv->coeff_half_len = ARRAY_LEN (slow_mid_qual_coeffs.coeffs) - 2 ;
            priv->index_inc = slow_mid_qual_coeffs.increment ;
            break ;
#endif
#ifdef ENABLE_SINC_BEST_CONVERTER
        case SRC_SINC_BEST_QUALITY :
            priv->coeffs = slow_high_qual_coeffs.coeffs ;
            priv->coeff_half_len = ARRAY_LEN (slow_high_qual_coeffs.coeffs) - 2 ;
            priv->index_inc = slow_high_qual_coeffs.increment ;
            break ;
#endif
        }

        priv->b_len = 3 * (int) psf_lrint ((priv->coeff_half_len + 2.0) / priv->index_inc * SRC_MAX_RATIO + 1) ;
        priv->b_len = MAX (priv->b_len, 4096) ;
        priv->b_len *= channels ;
        priv->b_len += 1 ; // There is a <= check against samples_in_hand requiring a buffer bigger than the calculation above


        priv->buffer = (float *) calloc (priv->b_len + channels, sizeof (float)) ;
        if (!priv->buffer)
        {
            free (priv) ;
            priv = NULL ;
        }
    }

    return priv ;
}

LIBSAMPLERATE_DLL_PRIVATE SRC_STATE *
sinc_state_new (int converter_type, int channels, SRC_ERROR *error)
{
    assert (converter_type == SRC_SINC_FASTEST ||
        converter_type == SRC_SINC_MEDIUM_QUALITY ||
        converter_type == SRC_SINC_BEST_QUALITY) ;
    assert (channels > 0) ;
    assert (error != NULL) ;

    if (channels > MAX_CHANNELS)
    {
        *error = SRC_ERR_BAD_CHANNEL_COUNT ;
        return NULL ;
    }

    SRC_STATE *state = (SRC_STATE *) calloc (1, sizeof (SRC_STATE)) ;
    if (!state)
    {
        *error = SRC_ERR_MALLOC_FAILED ;
        return NULL ;
    }

    state->channels = channels ;
    state->mode = SRC_MODE_PROCESS ;

    if (state->channels == 1)
        state->vt = &sinc_mono_state_vt ;
    else if (state->channels == 2)
        state->vt = &sinc_stereo_state_vt ;
    else if (state->channels == 4)
        state->vt = &sinc_quad_state_vt ;
    else if (state->channels == 6)
        state->vt = &sinc_hex_state_vt ;
    else
        state->vt = &sinc_multichan_state_vt ;

    state->private_data = sinc_filter_new (converter_type, state->channels) ;
    if (!state->private_data)
    {
        free (state) ;
        *error = SRC_ERR_MALLOC_FAILED ;
        return NULL ;
    }

    sinc_reset (state) ;

    *error = SRC_ERR_NO_ERROR ;

    return state ;
}

static void
sinc_reset (SRC_STATE *state)
{   SINC_FILTER *filter ;

    filter = (SINC_FILTER*) state->private_data ;
    if (filter == NULL)
        return ;

    filter->b_current = filter->b_end = 0 ;
    filter->b_real_end = -1 ;

    filter->src_ratio = filter->input_index = 0.0 ;

    memset (filter->buffer, 0, filter->b_len * sizeof (filter->buffer [0])) ;

    /* Set this for a sanity check */
    memset (filter->buffer + filter->b_len, 0xAA, state->channels * sizeof (filter->buffer [0])) ;
} /* sinc_reset */

static SRC_STATE *
sinc_copy (SRC_STATE *state)
{
    assert (state != NULL) ;

    if (state->private_data == NULL)
        return NULL ;

    SRC_STATE *to = (SRC_STATE *) calloc (1, sizeof (SRC_STATE)) ;
    if (!to)
        return NULL ;
    memcpy (to, state, sizeof (SRC_STATE)) ;


    SINC_FILTER* from_filter = (SINC_FILTER*) state->private_data ;
    SINC_FILTER *to_filter = (SINC_FILTER *) calloc (1, sizeof (SINC_FILTER)) ;
    if (!to_filter)
    {
        free (to) ;
        return NULL ;
    }
    memcpy (to_filter, from_filter, sizeof (SINC_FILTER)) ;
    to_filter->buffer = (float *) malloc (sizeof (float) * (from_filter->b_len + state->channels)) ;
    if (!to_filter->buffer)
    {
        free (to) ;
        free (to_filter) ;
        return NULL ;
    }
    memcpy (to_filter->buffer, from_filter->buffer, sizeof (float) * (from_filter->b_len + state->channels)) ;

    to->private_data = to_filter ;

    return to ;
} /* sinc_copy */

/*========================================================================================
**  Beware all ye who dare pass this point. There be dragons here.
*/

static inline double
calc_output_single (SINC_FILTER *filter, increment_t increment, increment_t start_filter_index)
{   double      fraction, left, right, icoeff ;
    increment_t filter_index, max_filter_index ;
    int         data_index, coeff_count, indx ;

    /* Convert input parameters into fixed point. */
    max_filter_index = int_to_fp (filter->coeff_half_len) ;

    /* First apply the left half of the filter. */
    filter_index = start_filter_index ;
    coeff_count = (max_filter_index - filter_index) / increment ;
    filter_index = filter_index + coeff_count * increment ;
    data_index = filter->b_current - coeff_count ;

    if (data_index < 0) /* Avoid underflow access to filter->buffer. */
    {   int steps = -data_index ;
        /* If the assert triggers we would have to take care not to underflow/overflow */
        assert (steps <= int_div_ceil (filter_index, increment)) ;
        filter_index -= increment * steps ;
        data_index += steps ;
    }
    left = 0.0 ;
    while (filter_index >= MAKE_INCREMENT_T (0))
    {   fraction = fp_to_double (filter_index) ;
        indx = fp_to_int (filter_index) ;
        assert (indx >= 0 && indx + 1 < filter->coeff_half_len + 2) ;
        icoeff = filter->coeffs [indx] + fraction * (filter->coeffs [indx + 1] - filter->coeffs [indx]) ;
        assert (data_index >= 0 && data_index < filter->b_len) ;
        assert (data_index < filter->b_end) ;
        left += icoeff * filter->buffer [data_index] ;

        filter_index -= increment ;
        data_index = data_index + 1 ;
        } ;

    /* Now apply the right half of the filter. */
    filter_index = increment - start_filter_index ;
    coeff_count = (max_filter_index - filter_index) / increment ;
    filter_index = filter_index + coeff_count * increment ;
    data_index = filter->b_current + 1 + coeff_count ;

    right = 0.0 ;
    do
    {   fraction = fp_to_double (filter_index) ;
        indx = fp_to_int (filter_index) ;
        assert (indx < filter->coeff_half_len + 2) ;
        icoeff = filter->coeffs [indx] + fraction * (filter->coeffs [indx + 1] - filter->coeffs [indx]) ;
        assert (data_index >= 0 && data_index < filter->b_len) ;
        assert (data_index < filter->b_end) ;
        right += icoeff * filter->buffer [data_index] ;

        filter_index -= increment ;
        data_index = data_index - 1 ;
        }
    while (filter_index > MAKE_INCREMENT_T (0)) ;

    return (left + right) ;
} /* calc_output_single */

static SRC_ERROR
sinc_mono_vari_process (SRC_STATE *state, SRC_DATA *data)
{   SINC_FILTER *filter ;
    double      input_index, src_ratio, count, float_increment, terminate, rem ;
    increment_t increment, start_filter_index ;
    int         half_filter_chan_len, samples_in_hand ;

    if (state->private_data == NULL)
        return SRC_ERR_NO_PRIVATE ;

    filter = (SINC_FILTER*) state->private_data ;

    /* If there is not a problem, this will be optimised out. */
    if (sizeof (filter->buffer [0]) != sizeof (data->data_in [0]))
        return SRC_ERR_SIZE_INCOMPATIBILITY ;

    filter->in_count = data->input_frames * state->channels ;
    filter->out_count = data->output_frames * state->channels ;
    filter->in_used = filter->out_gen = 0 ;

    src_ratio = state->last_ratio ;

    if (is_bad_src_ratio (src_ratio))
        return SRC_ERR_BAD_INTERNAL_STATE ;

    /* Check the sample rate ratio wrt the buffer len. */
    count = (filter->coeff_half_len + 2.0) / filter->index_inc ;
    if (MIN (state->last_ratio, data->src_ratio) < 1.0)
        count /= MIN (state->last_ratio, data->src_ratio) ;

    /* Maximum coefficientson either side of center point. */
    half_filter_chan_len = state->channels * (int) (psf_lrint (count) + 1) ;

    input_index = state->last_position ;

    rem = fmod_one (input_index) ;
    filter->b_current = (filter->b_current + state->channels * psf_lrint (input_index - rem)) % filter->b_len ;
    input_index = rem ;

    terminate = 1.0 / src_ratio + 1e-20 ;

    /* Main processing loop. */
    while (filter->out_gen < filter->out_count)
    {
        /* Need to reload buffer? */
        samples_in_hand = (filter->b_end - filter->b_current + filter->b_len) % filter->b_len ;

        if (samples_in_hand <= half_filter_chan_len)
        {   if ((state->error = prepare_data (filter, state->channels, data, half_filter_chan_len)) != 0)
                return state->error ;

            samples_in_hand = (filter->b_end - filter->b_current + filter->b_len) % filter->b_len ;
            if (samples_in_hand <= half_filter_chan_len)
                break ;
            } ;

        /* This is the termination condition. */
        if (filter->b_real_end >= 0)
        {   if (filter->b_current + input_index + terminate > filter->b_real_end)
                break ;
            } ;

        if (filter->out_count > 0 && fabs (state->last_ratio - data->src_ratio) > 1e-10)
            src_ratio = state->last_ratio + filter->out_gen * (data->src_ratio - state->last_ratio) / filter->out_count ;

        float_increment = filter->index_inc * (src_ratio < 1.0 ? src_ratio : 1.0) ;
        increment = double_to_fp (float_increment) ;

        start_filter_index = double_to_fp (input_index * float_increment) ;

        data->data_out [filter->out_gen] = (float) ((float_increment / filter->index_inc) *
                                        calc_output_single (filter, increment, start_filter_index)) ;
        filter->out_gen ++ ;

        /* Figure out the next index. */
        input_index += 1.0 / src_ratio ;
        rem = fmod_one (input_index) ;

        filter->b_current = (filter->b_current + state->channels * psf_lrint (input_index - rem)) % filter->b_len ;
        input_index = rem ;
        } ;

    state->last_position = input_index ;

    /* Save current ratio rather then target ratio. */
    state->last_ratio = src_ratio ;

    data->input_frames_used = filter->in_used / state->channels ;
    data->output_frames_gen = filter->out_gen / state->channels ;

    return SRC_ERR_NO_ERROR ;
} /* sinc_mono_vari_process */

static inline void
calc_output_stereo (SINC_FILTER *filter, int channels, increment_t increment, increment_t start_filter_index, double scale, float * output)
{   double      fraction, left [2], right [2], icoeff ;
    increment_t filter_index, max_filter_index ;
    int         data_index, coeff_count, indx ;

    /* Convert input parameters into fixed point. */
    max_filter_index = int_to_fp (filter->coeff_half_len) ;

    /* First apply the left half of the filter. */
    filter_index = start_filter_index ;
    coeff_count = (max_filter_index - filter_index) / increment ;
    filter_index = filter_index + coeff_count * increment ;
    data_index = filter->b_current - channels * coeff_count ;

    if (data_index < 0) /* Avoid underflow access to filter->buffer. */
    {   int steps = int_div_ceil (-data_index, 2) ;
        /* If the assert triggers we would have to take care not to underflow/overflow */
        assert (steps <= int_div_ceil (filter_index, increment)) ;
        filter_index -= increment * steps ;
        data_index += steps * 2;
    }
    left [0] = left [1] = 0.0 ;
    while (filter_index >= MAKE_INCREMENT_T (0))
    {   fraction = fp_to_double (filter_index) ;
        indx = fp_to_int (filter_index) ;
        assert (indx >= 0 && indx + 1 < filter->coeff_half_len + 2) ;
        icoeff = filter->coeffs [indx] + fraction * (filter->coeffs [indx + 1] - filter->coeffs [indx]) ;
        assert (data_index >= 0 && data_index + 1 < filter->b_len) ;
        assert (data_index + 1 < filter->b_end) ;
        for (int ch = 0; ch < 2; ch++)
            left [ch] += icoeff * filter->buffer [data_index + ch] ;

        filter_index -= increment ;
        data_index = data_index + 2 ;
        } ;

    /* Now apply the right half of the filter. */
    filter_index = increment - start_filter_index ;
    coeff_count = (max_filter_index - filter_index) / increment ;
    filter_index = filter_index + coeff_count * increment ;
    data_index = filter->b_current + channels * (1 + coeff_count) ;

    right [0] = right [1] = 0.0 ;
    do
    {   fraction = fp_to_double (filter_index) ;
        indx = fp_to_int (filter_index) ;
        assert (indx >= 0 && indx + 1 < filter->coeff_half_len + 2) ;
        icoeff = filter->coeffs [indx] + fraction * (filter->coeffs [indx + 1] - filter->coeffs [indx]) ;
        assert (data_index >= 0 && data_index + 1 < filter->b_len) ;
        assert (data_index + 1 < filter->b_end) ;
        for (int ch = 0; ch < 2; ch++)
            right [ch] += icoeff * filter->buffer [data_index + ch] ;

        filter_index -= increment ;
        data_index = data_index - 2 ;
        }
    while (filter_index > MAKE_INCREMENT_T (0)) ;

    for (int ch = 0; ch < 2; ch++)
        output [ch] = (float) (scale * (left [ch] + right [ch])) ;
} /* calc_output_stereo */

SRC_ERROR
sinc_stereo_vari_process (SRC_STATE *state, SRC_DATA *data)
{   SINC_FILTER *filter ;
    double      input_index, src_ratio, count, float_increment, terminate, rem ;
    increment_t increment, start_filter_index ;
    int         half_filter_chan_len, samples_in_hand ;

    if (state->private_data == NULL)
        return SRC_ERR_NO_PRIVATE ;

    filter = (SINC_FILTER*) state->private_data ;

    /* If there is not a problem, this will be optimised out. */
    if (sizeof (filter->buffer [0]) != sizeof (data->data_in [0]))
        return SRC_ERR_SIZE_INCOMPATIBILITY ;

    filter->in_count = data->input_frames * state->channels ;
    filter->out_count = data->output_frames * state->channels ;
    filter->in_used = filter->out_gen = 0 ;

    src_ratio = state->last_ratio ;

    if (is_bad_src_ratio (src_ratio))
        return SRC_ERR_BAD_INTERNAL_STATE ;

    /* Check the sample rate ratio wrt the buffer len. */
    count = (filter->coeff_half_len + 2.0) / filter->index_inc ;
    if (MIN (state->last_ratio, data->src_ratio) < 1.0)
        count /= MIN (state->last_ratio, data->src_ratio) ;

    /* Maximum coefficientson either side of center point. */
    half_filter_chan_len = state->channels * (int) (psf_lrint (count) + 1) ;

    input_index = state->last_position ;

    rem = fmod_one (input_index) ;
    filter->b_current = (filter->b_current + state->channels * psf_lrint (input_index - rem)) % filter->b_len ;
    input_index = rem ;

    terminate = 1.0 / src_ratio + 1e-20 ;

    /* Main processing loop. */
    while (filter->out_gen < filter->out_count)
    {
        /* Need to reload buffer? */
        samples_in_hand = (filter->b_end - filter->b_current + filter->b_len) % filter->b_len ;

        if (samples_in_hand <= half_filter_chan_len)
        {   if ((state->error = prepare_data (filter, state->channels, data, half_filter_chan_len)) != 0)
                return state->error ;

            samples_in_hand = (filter->b_end - filter->b_current + filter->b_len) % filter->b_len ;
            if (samples_in_hand <= half_filter_chan_len)
                break ;
            } ;

        /* This is the termination condition. */
        if (filter->b_real_end >= 0)
        {   if (filter->b_current + input_index + terminate >= filter->b_real_end)
                break ;
            } ;

        if (filter->out_count > 0 && fabs (state->last_ratio - data->src_ratio) > 1e-10)
            src_ratio = state->last_ratio + filter->out_gen * (data->src_ratio - state->last_ratio) / filter->out_count ;

        float_increment = filter->index_inc * (src_ratio < 1.0 ? src_ratio : 1.0) ;
        increment = double_to_fp (float_increment) ;

        start_filter_index = double_to_fp (input_index * float_increment) ;

        calc_output_stereo (filter, state->channels, increment, start_filter_index, float_increment / filter->index_inc, data->data_out + filter->out_gen) ;
        filter->out_gen += 2 ;

        /* Figure out the next index. */
        input_index += 1.0 / src_ratio ;
        rem = fmod_one (input_index) ;

        filter->b_current = (filter->b_current + state->channels * psf_lrint (input_index - rem)) % filter->b_len ;
        input_index = rem ;
        } ;

    state->last_position = input_index ;

    /* Save current ratio rather then target ratio. */
    state->last_ratio = src_ratio ;

    data->input_frames_used = filter->in_used / state->channels ;
    data->output_frames_gen = filter->out_gen / state->channels ;

    return SRC_ERR_NO_ERROR ;
} /* sinc_stereo_vari_process */

static inline void
calc_output_quad (SINC_FILTER *filter, int channels, increment_t increment, increment_t start_filter_index, double scale, float * output)
{   double      fraction, left [4], right [4], icoeff ;
    increment_t filter_index, max_filter_index ;
    int         data_index, coeff_count, indx ;

    /* Convert input parameters into fixed point. */
    max_filter_index = int_to_fp (filter->coeff_half_len) ;

    /* First apply the left half of the filter. */
    filter_index = start_filter_index ;
    coeff_count = (max_filter_index - filter_index) / increment ;
    filter_index = filter_index + coeff_count * increment ;
    data_index = filter->b_current - channels * coeff_count ;

    if (data_index < 0) /* Avoid underflow access to filter->buffer. */
    {   int steps = int_div_ceil (-data_index, 4) ;
        /* If the assert triggers we would have to take care not to underflow/overflow */
        assert (steps <= int_div_ceil (filter_index, increment)) ;
        filter_index -= increment * steps ;
        data_index += steps * 4;
    }
    left [0] = left [1] = left [2] = left [3] = 0.0 ;
    while (filter_index >= MAKE_INCREMENT_T (0))
    {   fraction = fp_to_double (filter_index) ;
        indx = fp_to_int (filter_index) ;
        assert (indx >= 0 && indx + 1 < filter->coeff_half_len + 2) ;
        icoeff = filter->coeffs [indx] + fraction * (filter->coeffs [indx + 1] - filter->coeffs [indx]) ;
        assert (data_index >= 0 && data_index + 3 < filter->b_len) ;
        assert (data_index + 3 < filter->b_end) ;
        for (int ch = 0; ch < 4; ch++)
            left [ch] += icoeff * filter->buffer [data_index + ch] ;

        filter_index -= increment ;
        data_index = data_index + 4 ;
        } ;

    /* Now apply the right half of the filter. */
    filter_index = increment - start_filter_index ;
    coeff_count = (max_filter_index - filter_index) / increment ;
    filter_index = filter_index + coeff_count * increment ;
    data_index = filter->b_current + channels * (1 + coeff_count) ;

    right [0] = right [1] = right [2] = right [3] = 0.0 ;
    do
    {   fraction = fp_to_double (filter_index) ;
        indx = fp_to_int (filter_index) ;
        assert (indx >= 0 && indx + 1 < filter->coeff_half_len + 2) ;
        icoeff = filter->coeffs [indx] + fraction * (filter->coeffs [indx + 1] - filter->coeffs [indx]) ;
        assert (data_index >= 0 && data_index + 3 < filter->b_len) ;
        assert (data_index + 3 < filter->b_end) ;
        for (int ch = 0; ch < 4; ch++)
            right [ch] += icoeff * filter->buffer [data_index + ch] ;


        filter_index -= increment ;
        data_index = data_index - 4 ;
        }
    while (filter_index > MAKE_INCREMENT_T (0)) ;

    for (int ch = 0; ch < 4; ch++)
        output [ch] = (float) (scale * (left [ch] + right [ch])) ;
} /* calc_output_quad */

SRC_ERROR
sinc_quad_vari_process (SRC_STATE *state, SRC_DATA *data)
{   SINC_FILTER *filter ;
    double      input_index, src_ratio, count, float_increment, terminate, rem ;
    increment_t increment, start_filter_index ;
    int         half_filter_chan_len, samples_in_hand ;

    if (state->private_data == NULL)
        return SRC_ERR_NO_PRIVATE ;

    filter = (SINC_FILTER*) state->private_data ;

    /* If there is not a problem, this will be optimised out. */
    if (sizeof (filter->buffer [0]) != sizeof (data->data_in [0]))
        return SRC_ERR_SIZE_INCOMPATIBILITY ;

    filter->in_count = data->input_frames * state->channels ;
    filter->out_count = data->output_frames * state->channels ;
    filter->in_used = filter->out_gen = 0 ;

    src_ratio = state->last_ratio ;

    if (is_bad_src_ratio (src_ratio))
        return SRC_ERR_BAD_INTERNAL_STATE ;

    /* Check the sample rate ratio wrt the buffer len. */
    count = (filter->coeff_half_len + 2.0) / filter->index_inc ;
    if (MIN (state->last_ratio, data->src_ratio) < 1.0)
        count /= MIN (state->last_ratio, data->src_ratio) ;

    /* Maximum coefficientson either side of center point. */
    half_filter_chan_len = state->channels * (int) (psf_lrint (count) + 1) ;

    input_index = state->last_position ;

    rem = fmod_one (input_index) ;
    filter->b_current = (filter->b_current + state->channels * psf_lrint (input_index - rem)) % filter->b_len ;
    input_index = rem ;

    terminate = 1.0 / src_ratio + 1e-20 ;

    /* Main processing loop. */
    while (filter->out_gen < filter->out_count)
    {
        /* Need to reload buffer? */
        samples_in_hand = (filter->b_end - filter->b_current + filter->b_len) % filter->b_len ;

        if (samples_in_hand <= half_filter_chan_len)
        {   if ((state->error = prepare_data (filter, state->channels, data, half_filter_chan_len)) != 0)
                return state->error ;

            samples_in_hand = (filter->b_end - filter->b_current + filter->b_len) % filter->b_len ;
            if (samples_in_hand <= half_filter_chan_len)
                break ;
            } ;

        /* This is the termination condition. */
        if (filter->b_real_end >= 0)
        {   if (filter->b_current + input_index + terminate >= filter->b_real_end)
                break ;
            } ;

        if (filter->out_count > 0 && fabs (state->last_ratio - data->src_ratio) > 1e-10)
            src_ratio = state->last_ratio + filter->out_gen * (data->src_ratio - state->last_ratio) / filter->out_count ;

        float_increment = filter->index_inc * (src_ratio < 1.0 ? src_ratio : 1.0) ;
        increment = double_to_fp (float_increment) ;

        start_filter_index = double_to_fp (input_index * float_increment) ;

        calc_output_quad (filter, state->channels, increment, start_filter_index, float_increment / filter->index_inc, data->data_out + filter->out_gen) ;
        filter->out_gen += 4 ;

        /* Figure out the next index. */
        input_index += 1.0 / src_ratio ;
        rem = fmod_one (input_index) ;

        filter->b_current = (filter->b_current + state->channels * psf_lrint (input_index - rem)) % filter->b_len ;
        input_index = rem ;
        } ;

    state->last_position = input_index ;

    /* Save current ratio rather then target ratio. */
    state->last_ratio = src_ratio ;

    data->input_frames_used = filter->in_used / state->channels ;
    data->output_frames_gen = filter->out_gen / state->channels ;

    return SRC_ERR_NO_ERROR ;
} /* sinc_quad_vari_process */

static inline void
calc_output_hex (SINC_FILTER *filter, int channels, increment_t increment, increment_t start_filter_index, double scale, float * output)
{   double      fraction, left [6], right [6], icoeff ;
    increment_t filter_index, max_filter_index ;
    int         data_index, coeff_count, indx ;

    /* Convert input parameters into fixed point. */
    max_filter_index = int_to_fp (filter->coeff_half_len) ;

    /* First apply the left half of the filter. */
    filter_index = start_filter_index ;
    coeff_count = (max_filter_index - filter_index) / increment ;
    filter_index = filter_index + coeff_count * increment ;
    data_index = filter->b_current - channels * coeff_count ;

    if (data_index < 0) /* Avoid underflow access to filter->buffer. */
    {   int steps = int_div_ceil (-data_index, 6) ;
        /* If the assert triggers we would have to take care not to underflow/overflow */
        assert (steps <= int_div_ceil (filter_index, increment)) ;
        filter_index -= increment * steps ;
        data_index += steps * 6;
    }
    left [0] = left [1] = left [2] = left [3] = left [4] = left [5] = 0.0 ;
    while (filter_index >= MAKE_INCREMENT_T (0))
    {   fraction = fp_to_double (filter_index) ;
        indx = fp_to_int (filter_index) ;
        assert (indx >= 0 && indx + 1 < filter->coeff_half_len + 2) ;
        icoeff = filter->coeffs [indx] + fraction * (filter->coeffs [indx + 1] - filter->coeffs [indx]) ;
        assert (data_index >= 0 && data_index + 5 < filter->b_len) ;
        assert (data_index + 5 < filter->b_end) ;
        for (int ch = 0; ch < 6; ch++)
            left [ch] += icoeff * filter->buffer [data_index + ch] ;

        filter_index -= increment ;
        data_index = data_index + 6 ;
        } ;

    /* Now apply the right half of the filter. */
    filter_index = increment - start_filter_index ;
    coeff_count = (max_filter_index - filter_index) / increment ;
    filter_index = filter_index + coeff_count * increment ;
    data_index = filter->b_current + channels * (1 + coeff_count) ;

    right [0] = right [1] = right [2] = right [3] = right [4] = right [5] = 0.0 ;
    do
    {   fraction = fp_to_double (filter_index) ;
        indx = fp_to_int (filter_index) ;
        assert (indx >= 0 && indx + 1 < filter->coeff_half_len + 2) ;
        icoeff = filter->coeffs [indx] + fraction * (filter->coeffs [indx + 1] - filter->coeffs [indx]) ;
        assert (data_index >= 0 && data_index + 5 < filter->b_len) ;
        assert (data_index + 5 < filter->b_end) ;
        for (int ch = 0; ch < 6; ch++)
            right [ch] += icoeff * filter->buffer [data_index + ch] ;

        filter_index -= increment ;
        data_index = data_index - 6 ;
        }
    while (filter_index > MAKE_INCREMENT_T (0)) ;

    for (int ch = 0; ch < 6; ch++)
        output [ch] = (float) (scale * (left [ch] + right [ch])) ;
} /* calc_output_hex */

SRC_ERROR
sinc_hex_vari_process (SRC_STATE *state, SRC_DATA *data)
{   SINC_FILTER *filter ;
    double      input_index, src_ratio, count, float_increment, terminate, rem ;
    increment_t increment, start_filter_index ;
    int         half_filter_chan_len, samples_in_hand ;

    if (state->private_data == NULL)
        return SRC_ERR_NO_PRIVATE ;

    filter = (SINC_FILTER*) state->private_data ;

    /* If there is not a problem, this will be optimised out. */
    if (sizeof (filter->buffer [0]) != sizeof (data->data_in [0]))
        return SRC_ERR_SIZE_INCOMPATIBILITY ;

    filter->in_count = data->input_frames * state->channels ;
    filter->out_count = data->output_frames * state->channels ;
    filter->in_used = filter->out_gen = 0 ;

    src_ratio = state->last_ratio ;

    if (is_bad_src_ratio (src_ratio))
        return SRC_ERR_BAD_INTERNAL_STATE ;

    /* Check the sample rate ratio wrt the buffer len. */
    count = (filter->coeff_half_len + 2.0) / filter->index_inc ;
    if (MIN (state->last_ratio, data->src_ratio) < 1.0)
        count /= MIN (state->last_ratio, data->src_ratio) ;

    /* Maximum coefficientson either side of center point. */
    half_filter_chan_len = state->channels * (int) (psf_lrint (count) + 1) ;

    input_index = state->last_position ;

    rem = fmod_one (input_index) ;
    filter->b_current = (filter->b_current + state->channels * psf_lrint (input_index - rem)) % filter->b_len ;
    input_index = rem ;

    terminate = 1.0 / src_ratio + 1e-20 ;

    /* Main processing loop. */
    while (filter->out_gen < filter->out_count)
    {
        /* Need to reload buffer? */
        samples_in_hand = (filter->b_end - filter->b_current + filter->b_len) % filter->b_len ;

        if (samples_in_hand <= half_filter_chan_len)
        {   if ((state->error = prepare_data (filter, state->channels, data, half_filter_chan_len)) != 0)
                return state->error ;

            samples_in_hand = (filter->b_end - filter->b_current + filter->b_len) % filter->b_len ;
            if (samples_in_hand <= half_filter_chan_len)
                break ;
            } ;

        /* This is the termination condition. */
        if (filter->b_real_end >= 0)
        {   if (filter->b_current + input_index + terminate >= filter->b_real_end)
                break ;
            } ;

        if (filter->out_count > 0 && fabs (state->last_ratio - data->src_ratio) > 1e-10)
            src_ratio = state->last_ratio + filter->out_gen * (data->src_ratio - state->last_ratio) / filter->out_count ;

        float_increment = filter->index_inc * (src_ratio < 1.0 ? src_ratio : 1.0) ;
        increment = double_to_fp (float_increment) ;

        start_filter_index = double_to_fp (input_index * float_increment) ;

        calc_output_hex (filter, state->channels, increment, start_filter_index, float_increment / filter->index_inc, data->data_out + filter->out_gen) ;
        filter->out_gen += 6 ;

        /* Figure out the next index. */
        input_index += 1.0 / src_ratio ;
        rem = fmod_one (input_index) ;

        filter->b_current = (filter->b_current + state->channels * psf_lrint (input_index - rem)) % filter->b_len ;
        input_index = rem ;
        } ;

    state->last_position = input_index ;

    /* Save current ratio rather then target ratio. */
    state->last_ratio = src_ratio ;

    data->input_frames_used = filter->in_used / state->channels ;
    data->output_frames_gen = filter->out_gen / state->channels ;

    return SRC_ERR_NO_ERROR ;
} /* sinc_hex_vari_process */

static inline void
calc_output_multi (SINC_FILTER *filter, increment_t increment, increment_t start_filter_index, int channels, double scale, float * output)
{   double      fraction, icoeff ;
    /* The following line is 1999 ISO Standard C. If your compiler complains, get a better compiler. */
    double      *left, *right ;
    increment_t filter_index, max_filter_index ;
    int         data_index, coeff_count, indx ;

    left = filter->left_calc ;
    right = filter->right_calc ;

    /* Convert input parameters into fixed point. */
    max_filter_index = int_to_fp (filter->coeff_half_len) ;

    /* First apply the left half of the filter. */
    filter_index = start_filter_index ;
    coeff_count = (max_filter_index - filter_index) / increment ;
    filter_index = filter_index + coeff_count * increment ;
    data_index = filter->b_current - channels * coeff_count ;

    if (data_index < 0) /* Avoid underflow access to filter->buffer. */
    {   int steps = int_div_ceil (-data_index, channels) ;
        /* If the assert triggers we would have to take care not to underflow/overflow */
        assert (steps <= int_div_ceil (filter_index, increment)) ;
        filter_index -= increment * steps ;
        data_index += steps * channels ;
    }

    memset (left, 0, sizeof (left [0]) * channels) ;

    while (filter_index >= MAKE_INCREMENT_T (0))
    {   fraction = fp_to_double (filter_index) ;
        indx = fp_to_int (filter_index) ;
        assert (indx >= 0 && indx + 1 < filter->coeff_half_len + 2) ;
        icoeff = filter->coeffs [indx] + fraction * (filter->coeffs [indx + 1] - filter->coeffs [indx]) ;

        assert (data_index >= 0 && data_index + channels - 1 < filter->b_len) ;
        assert (data_index + channels - 1 < filter->b_end) ;
        for (int ch = 0; ch < channels; ch++)
            left [ch] += icoeff * filter->buffer [data_index + ch] ;

        filter_index -= increment ;
        data_index = data_index + channels ;
        } ;

    /* Now apply the right half of the filter. */
    filter_index = increment - start_filter_index ;
    coeff_count = (max_filter_index - filter_index) / increment ;
    filter_index = filter_index + coeff_count * increment ;
    data_index = filter->b_current + channels * (1 + coeff_count) ;

    memset (right, 0, sizeof (right [0]) * channels) ;
    do
    {   fraction = fp_to_double (filter_index) ;
        indx = fp_to_int (filter_index) ;
        assert (indx >= 0 && indx + 1 < filter->coeff_half_len + 2) ;
        icoeff = filter->coeffs [indx] + fraction * (filter->coeffs [indx + 1] - filter->coeffs [indx]) ;
        assert (data_index >= 0 && data_index + channels - 1 < filter->b_len) ;
        assert (data_index + channels - 1 < filter->b_end) ;
        for (int ch = 0; ch < channels; ch++)
            right [ch] += icoeff * filter->buffer [data_index + ch] ;

        filter_index -= increment ;
        data_index = data_index - channels ;
        }
    while (filter_index > MAKE_INCREMENT_T (0)) ;

    for(int ch = 0; ch < channels; ch++)
        output [ch] = (float) (scale * (left [ch] + right [ch])) ;

    return ;
} /* calc_output_multi */

static SRC_ERROR
sinc_multichan_vari_process (SRC_STATE *state, SRC_DATA *data)
{   SINC_FILTER *filter ;
    double      input_index, src_ratio, count, float_increment, terminate, rem ;
    increment_t increment, start_filter_index ;
    int         half_filter_chan_len, samples_in_hand ;

    if (state->private_data == NULL)
        return SRC_ERR_NO_PRIVATE ;

    filter = (SINC_FILTER*) state->private_data ;

    /* If there is not a problem, this will be optimised out. */
    if (sizeof (filter->buffer [0]) != sizeof (data->data_in [0]))
        return SRC_ERR_SIZE_INCOMPATIBILITY ;

    filter->in_count = data->input_frames * state->channels ;
    filter->out_count = data->output_frames * state->channels ;
    filter->in_used = filter->out_gen = 0 ;

    src_ratio = state->last_ratio ;

    if (is_bad_src_ratio (src_ratio))
        return SRC_ERR_BAD_INTERNAL_STATE ;

    /* Check the sample rate ratio wrt the buffer len. */
    count = (filter->coeff_half_len + 2.0) / filter->index_inc ;
    if (MIN (state->last_ratio, data->src_ratio) < 1.0)
        count /= MIN (state->last_ratio, data->src_ratio) ;

    /* Maximum coefficientson either side of center point. */
    half_filter_chan_len = state->channels * (int) (psf_lrint (count) + 1) ;

    input_index = state->last_position ;

    rem = fmod_one (input_index) ;
    filter->b_current = (filter->b_current + state->channels * psf_lrint (input_index - rem)) % filter->b_len ;
    input_index = rem ;

    terminate = 1.0 / src_ratio + 1e-20 ;

    /* Main processing loop. */
    while (filter->out_gen < filter->out_count)
    {
        /* Need to reload buffer? */
        samples_in_hand = (filter->b_end - filter->b_current + filter->b_len) % filter->b_len ;

        if (samples_in_hand <= half_filter_chan_len)
        {   if ((state->error = prepare_data (filter, state->channels, data, half_filter_chan_len)) != 0)
                return state->error ;

            samples_in_hand = (filter->b_end - filter->b_current + filter->b_len) % filter->b_len ;
            if (samples_in_hand <= half_filter_chan_len)
                break ;
            } ;

        /* This is the termination condition. */
        if (filter->b_real_end >= 0)
        {   if (filter->b_current + input_index + terminate >= filter->b_real_end)
                break ;
            } ;

        if (filter->out_count > 0 && fabs (state->last_ratio - data->src_ratio) > 1e-10)
            src_ratio = state->last_ratio + filter->out_gen * (data->src_ratio - state->last_ratio) / filter->out_count ;

        float_increment = filter->index_inc * (src_ratio < 1.0 ? src_ratio : 1.0) ;
        increment = double_to_fp (float_increment) ;

        start_filter_index = double_to_fp (input_index * float_increment) ;

        calc_output_multi (filter, increment, start_filter_index, state->channels, float_increment / filter->index_inc, data->data_out + filter->out_gen) ;
        filter->out_gen += state->channels ;

        /* Figure out the next index. */
        input_index += 1.0 / src_ratio ;
        rem = fmod_one (input_index) ;

        filter->b_current = (filter->b_current + state->channels * psf_lrint (input_index - rem)) % filter->b_len ;
        input_index = rem ;
        } ;

    state->last_position = input_index ;

    /* Save current ratio rather then target ratio. */
    state->last_ratio = src_ratio ;

    data->input_frames_used = filter->in_used / state->channels ;
    data->output_frames_gen = filter->out_gen / state->channels ;

    return SRC_ERR_NO_ERROR ;
} /* sinc_multichan_vari_process */

/*----------------------------------------------------------------------------------------
*/

static SRC_ERROR
prepare_data (SINC_FILTER *filter, int channels, SRC_DATA *data, int half_filter_chan_len)
{   int len = 0 ;

    if (filter->b_real_end >= 0)
        return SRC_ERR_NO_ERROR ;   /* Should be terminating. Just return. */

    if (data->data_in == NULL)
        return SRC_ERR_NO_ERROR ;

    if (filter->b_current == 0)
    {   /* Initial state. Set up zeros at the start of the buffer and
        ** then load new data after that.
        */
        len = filter->b_len - 2 * half_filter_chan_len ;

        filter->b_current = filter->b_end = half_filter_chan_len ;
        }
    else if (filter->b_end + half_filter_chan_len + channels < filter->b_len)
    {   /*  Load data at current end position. */
        len = MAX (filter->b_len - filter->b_current - half_filter_chan_len, 0) ;
        }
    else
    {   /* Move data at end of buffer back to the start of the buffer. */
        len = filter->b_end - filter->b_current ;
        memmove (filter->buffer, filter->buffer + filter->b_current - half_filter_chan_len,
                        (half_filter_chan_len + len) * sizeof (filter->buffer [0])) ;

        filter->b_current = half_filter_chan_len ;
        filter->b_end = filter->b_current + len ;

        /* Now load data at current end of buffer. */
        len = MAX (filter->b_len - filter->b_current - half_filter_chan_len, 0) ;
        } ;

    len = MIN ((int) (filter->in_count - filter->in_used), len) ;
    len -= (len % channels) ;

    if (len < 0 || filter->b_end + len > filter->b_len)
        return SRC_ERR_SINC_PREPARE_DATA_BAD_LEN ;

    memcpy (filter->buffer + filter->b_end, data->data_in + filter->in_used,
                        len * sizeof (filter->buffer [0])) ;

    filter->b_end += len ;
    filter->in_used += len ;

    if (filter->in_used == filter->in_count &&
            filter->b_end - filter->b_current < 2 * half_filter_chan_len && data->end_of_input)
    {   /* Handle the case where all data in the current buffer has been
        ** consumed and this is the last buffer.
        */

        if (filter->b_len - filter->b_end < half_filter_chan_len + 5)
        {   /* If necessary, move data down to the start of the buffer. */
            len = filter->b_end - filter->b_current ;
            memmove (filter->buffer, filter->buffer + filter->b_current - half_filter_chan_len,
                            (half_filter_chan_len + len) * sizeof (filter->buffer [0])) ;

            filter->b_current = half_filter_chan_len ;
            filter->b_end = filter->b_current + len ;
            } ;

        filter->b_real_end = filter->b_end ;
        len = half_filter_chan_len + 5 ;

        if (len < 0 || filter->b_end + len > filter->b_len)
            len = filter->b_len - filter->b_end ;

        memset (filter->buffer + filter->b_end, 0, len * sizeof (filter->buffer [0])) ;
        filter->b_end += len ;
        } ;

    return SRC_ERR_NO_ERROR ;
} /* prepare_data */

static void
sinc_close (SRC_STATE *state)
{
    if (state)
    {
        SINC_FILTER *sinc = (SINC_FILTER *) state->private_data ;
        if (sinc)
        {
            if (sinc->buffer)
            {
                free (sinc->buffer) ;
                sinc->buffer = NULL ;
            }
            free (sinc) ;
            sinc = NULL ;
        }
        free (state) ;
        state = NULL ;
    }
} /* sinc_close */
