src_zoh.c

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/*
** Copyright (c) 2002-2016, 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/erikd/libsamplerate/blob/master/COPYING
*/
 
#include "precomp.h"
 
static int zoh_vari_process (SRC_PRIVATE *psrc, SRC_DATA *data) ;
static void zoh_reset (SRC_PRIVATE *psrc) ;
 
/*========================================================================================
*/
 
#define ZOH_MAGIC_MARKER    MAKE_MAGIC ('s', 'r', 'c', 'z', 'o', 'h')
 
typedef struct
{   int     zoh_magic_marker ;
    int     channels ;
    int     reset ;
    long    in_count, in_used ;
    long    out_count, out_gen ;
    float   last_value [1] ;
} ZOH_DATA ;
 
/*----------------------------------------------------------------------------------------
*/
 
static int
zoh_vari_process (SRC_PRIVATE *psrc, SRC_DATA *data)
{   ZOH_DATA    *priv ;
    double      src_ratio, input_index, rem ;
    int         ch ;
 
    if (data->input_frames <= 0)
        return SRC_ERR_NO_ERROR ;
 
    if (psrc->private_data == NULL)
        return SRC_ERR_NO_PRIVATE ;
 
    priv = (ZOH_DATA*) psrc->private_data ;
 
    if (priv->reset)
    {   /* If we have just been reset, set the last_value data. */
        for (ch = 0 ; ch < priv->channels ; ch++)
            priv->last_value [ch] = data->data_in [ch] ;
        priv->reset = 0 ;
        } ;
 
    priv->in_count = data->input_frames * priv->channels ;
    priv->out_count = data->output_frames * priv->channels ;
    priv->in_used = priv->out_gen = 0 ;
 
    src_ratio = psrc->last_ratio ;
 
    if (is_bad_src_ratio (src_ratio))
        return SRC_ERR_BAD_INTERNAL_STATE ;
 
    input_index = psrc->last_position ;
 
    /* Calculate samples before first sample in input array. */
    while (input_index < 1.0 && priv->out_gen < priv->out_count)
    {
        if (priv->in_used + priv->channels * input_index >= priv->in_count)
            break ;
 
        if (priv->out_count > 0 && fabs (psrc->last_ratio - data->src_ratio) > SRC_MIN_RATIO_DIFF)
            src_ratio = psrc->last_ratio + priv->out_gen * (data->src_ratio - psrc->last_ratio) / priv->out_count ;
 
        for (ch = 0 ; ch < priv->channels ; ch++)
        {   data->data_out [priv->out_gen] = priv->last_value [ch] ;
            priv->out_gen ++ ;
            } ;
 
        /* Figure out the next index. */
        input_index += 1.0 / src_ratio ;
        } ;
 
    rem = fmod_one (input_index) ;
    priv->in_used += priv->channels * lrint (input_index - rem) ;
    input_index = rem ;
 
    /* Main processing loop. */
    while (priv->out_gen < priv->out_count && priv->in_used + priv->channels * input_index <= priv->in_count)
    {
        if (priv->out_count > 0 && fabs (psrc->last_ratio - data->src_ratio) > SRC_MIN_RATIO_DIFF)
            src_ratio = psrc->last_ratio + priv->out_gen * (data->src_ratio - psrc->last_ratio) / priv->out_count ;
 
        for (ch = 0 ; ch < priv->channels ; ch++)
        {   data->data_out [priv->out_gen] = data->data_in [priv->in_used - priv->channels + ch] ;
            priv->out_gen ++ ;
            } ;
 
        /* Figure out the next index. */
        input_index += 1.0 / src_ratio ;
        rem = fmod_one (input_index) ;
 
        priv->in_used += priv->channels * lrint (input_index - rem) ;
        input_index = rem ;
        } ;
 
    if (priv->in_used > priv->in_count)
    {   input_index += (priv->in_used - priv->in_count) / priv->channels ;
        priv->in_used = priv->in_count ;
        } ;
 
    psrc->last_position = input_index ;
 
    if (priv->in_used > 0)
        for (ch = 0 ; ch < priv->channels ; ch++)
            priv->last_value [ch] = data->data_in [priv->in_used - priv->channels + ch] ;
 
    /* Save current ratio rather then target ratio. */
    psrc->last_ratio = src_ratio ;
 
    data->input_frames_used = priv->in_used / priv->channels ;
    data->output_frames_gen = priv->out_gen / priv->channels ;
 
    return SRC_ERR_NO_ERROR ;
} /* zoh_vari_process */
 
/*------------------------------------------------------------------------------
*/
 
const char*
zoh_get_name (int src_enum)
{
    if (src_enum == SRC_ZERO_ORDER_HOLD)
        return "ZOH Interpolator" ;
 
    return NULL ;
} /* zoh_get_name */
 
const char*
zoh_get_description (int src_enum)
{
    if (src_enum == SRC_ZERO_ORDER_HOLD)
        return "Zero order hold interpolator, very fast, poor quality." ;
 
    return NULL ;
} /* zoh_get_descrition */
 
int
zoh_set_converter (SRC_PRIVATE *psrc, int src_enum)
{   ZOH_DATA *priv = NULL ;
 
    if (src_enum != SRC_ZERO_ORDER_HOLD)
        return SRC_ERR_BAD_CONVERTER ;
 
    if (psrc->private_data != NULL)
    {   free (psrc->private_data) ;
        psrc->private_data = NULL ;
        } ;
 
    if (psrc->private_data == NULL)
    {   priv = calloc (1, sizeof (*priv) + psrc->channels * sizeof (float)) ;
        psrc->private_data = priv ;
        } ;
 
    if (priv == NULL)
        return SRC_ERR_MALLOC_FAILED ;
 
    priv->zoh_magic_marker = ZOH_MAGIC_MARKER ;
    priv->channels = psrc->channels ;
 
    psrc->const_process = zoh_vari_process ;
    psrc->vari_process = zoh_vari_process ;
    psrc->reset = zoh_reset ;
 
    zoh_reset (psrc) ;
 
    return SRC_ERR_NO_ERROR ;
} /* zoh_set_converter */
 
/*===================================================================================
*/
 
static void
zoh_reset (SRC_PRIVATE *psrc)
{   ZOH_DATA *priv ;
 
    priv = (ZOH_DATA*) psrc->private_data ;
    if (priv == NULL)
        return ;
 
    priv->channels = psrc->channels ;
    priv->reset = 1 ;
    memset (priv->last_value, 0, sizeof (priv->last_value [0]) * priv->channels) ;
 
    return ;
} /* zoh_reset */