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filter.c

/* filter.c

   Free software by Richard W.E. Furse. Do with as you will. No
   warranty. 

   This LADSPA plugin provides simple (one poll) low-pass and
   high-pass filters implemented in C. 

   This file has poor memory protection. Failures during malloc() will
   not recover nicely. */

/*****************************************************************************/

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

/*****************************************************************************/

#include "ladspa.h"

/*****************************************************************************/

#define SF_CUTOFF  0
#define SF_INPUT   1
#define SF_OUTPUT  2

/*****************************************************************************/

/* Instance data for the simple filter. We can get away with using
   this structure for both low- and high-pass filters because the data
   stored is the same. Note that the actual run() calls differ
   however. */
typedef struct {

  LADSPA_Data m_fSampleRate;
  LADSPA_Data m_fTwoPiOverSampleRate;

  LADSPA_Data m_fLastOutput;
  LADSPA_Data m_fLastCutoff;
  LADSPA_Data m_fAmountOfCurrent;
  LADSPA_Data m_fAmountOfLast;

  /* Ports:
     ------ */

  LADSPA_Data * m_pfCutoff;
  LADSPA_Data * m_pfInput;
  LADSPA_Data * m_pfOutput;

} SimpleFilter;

/*****************************************************************************/

/* Construct a new plugin instance. In this case, as the SimpleFilter
   structure can be used for low- or high-pass filters we can get away
   with only only writing one of these functions. Normally one would
   be required for each plugin type. */
LADSPA_Handle 
instantiateSimpleFilter(const LADSPA_Descriptor * Descriptor,
                  unsigned long             SampleRate) {

  SimpleFilter * psFilter;

  psFilter = (SimpleFilter *)malloc(sizeof(SimpleFilter));

  if (psFilter) {
    psFilter->m_fSampleRate = (LADSPA_Data)SampleRate;
    psFilter->m_fTwoPiOverSampleRate = (2 * M_PI) / (LADSPA_Data)SampleRate;
    psFilter->m_fLastOutput = 0;
    psFilter->m_fLastCutoff = 0;
    psFilter->m_fAmountOfCurrent = 0;
    psFilter->m_fAmountOfLast = 0;
  }

  return psFilter;
}

/*****************************************************************************/

/* Initialise and activate a plugin instance. Normally separate
   functions would have to be written for the different plugin types,
   however we can get away with a single function in this case. */
void
activateSimpleFilter(LADSPA_Handle Instance) {
  SimpleFilter * psSimpleFilter;
  psSimpleFilter = (SimpleFilter *)Instance;
  psSimpleFilter->m_fLastOutput = 0;
}

/*****************************************************************************/

/* Connect a port to a data location. Normally separate functions
   would have to be written for the different plugin types, however we
   can get away with a single function in this case. */
void 
connectPortToSimpleFilter(LADSPA_Handle Instance,
                    unsigned long Port,
                    LADSPA_Data * DataLocation) {
  
  SimpleFilter * psFilter;

  psFilter = (SimpleFilter *)Instance;

  switch (Port) {
  case SF_CUTOFF:
    psFilter->m_pfCutoff = DataLocation;
    break;
  case SF_INPUT:
    psFilter->m_pfInput = DataLocation;
    break;
  case SF_OUTPUT:
    psFilter->m_pfOutput = DataLocation;
    break;
  }
}

/*****************************************************************************/

/* Run the LPF algorithm for a block of SampleCount samples. */
void 
runSimpleLowPassFilter(LADSPA_Handle Instance,
                   unsigned long SampleCount) {

  LADSPA_Data * pfInput;
  LADSPA_Data * pfOutput;
  LADSPA_Data fAmountOfCurrent;
  LADSPA_Data fAmountOfLast;
  LADSPA_Data fComp;
  LADSPA_Data fLastOutput;
  SimpleFilter * psFilter;
  unsigned long lSampleIndex;

  psFilter = (SimpleFilter *)Instance;

  pfInput = psFilter->m_pfInput;
  pfOutput = psFilter->m_pfOutput;

  if (*psFilter->m_pfCutoff != 
      psFilter->m_fLastCutoff) {
    psFilter->m_fLastCutoff = *psFilter->m_pfCutoff;
    if (psFilter->m_fLastCutoff <= 0) {
      /* Reject everything. */
      psFilter->m_fAmountOfCurrent = psFilter->m_fAmountOfLast = 0;
    }
    else if (psFilter->m_fLastCutoff > psFilter->m_fSampleRate * 0.5) {
      /* Above Nyquist frequency. Let everything through. */
      psFilter->m_fAmountOfCurrent = 1;
      psFilter->m_fAmountOfLast = 0;
    }
    else {
      psFilter->m_fAmountOfLast = 0;
      fComp = 2 - cos(psFilter->m_fTwoPiOverSampleRate
                  * psFilter->m_fLastCutoff);
      psFilter->m_fAmountOfLast     = fComp - (LADSPA_Data)sqrt(fComp * fComp - 1);
      psFilter->m_fAmountOfCurrent = 1 - psFilter->m_fAmountOfLast;
    }

  }

  fAmountOfCurrent = psFilter->m_fAmountOfCurrent;
  fAmountOfLast = psFilter->m_fAmountOfLast;
  fLastOutput = psFilter->m_fLastOutput;

  for (lSampleIndex = 0;
       lSampleIndex < SampleCount;
       lSampleIndex++) {
    *(pfOutput++)
      = fLastOutput
      = (fAmountOfCurrent * *(pfInput++)
       + fAmountOfLast * fLastOutput);
  }
  
  psFilter->m_fLastOutput = fLastOutput;
}

/*****************************************************************************/

/* Run the HPF algorithm for a block of SampleCount samples. */
void 
runSimpleHighPassFilter(LADSPA_Handle Instance,
                   unsigned long SampleCount) {

  LADSPA_Data * pfInput;
  LADSPA_Data * pfOutput;
  LADSPA_Data fAmountOfCurrent;
  LADSPA_Data fAmountOfLast;
  LADSPA_Data fComp;
  LADSPA_Data fLastOutput;
  SimpleFilter * psFilter;
  unsigned long lSampleIndex;

  psFilter = (SimpleFilter *)Instance;

  pfInput = psFilter->m_pfInput;
  pfOutput = psFilter->m_pfOutput;

  if (*psFilter->m_pfCutoff != 
      psFilter->m_fLastCutoff) {
    psFilter->m_fLastCutoff = *psFilter->m_pfCutoff;
    if (psFilter->m_fLastCutoff <= 0) {
      /* Let everything through. */
      psFilter->m_fAmountOfCurrent = 1;
      psFilter->m_fAmountOfLast = 0;
    }
    else if (psFilter->m_fLastCutoff > psFilter->m_fSampleRate * 0.5) {
      /* Above Nyquist frequency. Reject everything. */
      psFilter->m_fAmountOfCurrent = psFilter->m_fAmountOfLast = 0;
    }
    else {
      psFilter->m_fAmountOfLast = 0;
      fComp = 2 - cos(psFilter->m_fTwoPiOverSampleRate
                  * psFilter->m_fLastCutoff);
      psFilter->m_fAmountOfLast     = fComp - (LADSPA_Data)sqrt(fComp * fComp - 1);
      psFilter->m_fAmountOfCurrent = 1 - psFilter->m_fAmountOfLast;
    }

  }

  fAmountOfCurrent = psFilter->m_fAmountOfCurrent;
  fAmountOfLast = psFilter->m_fAmountOfLast;
  fLastOutput = psFilter->m_fLastOutput;

  for (lSampleIndex = 0;
       lSampleIndex < SampleCount;
       lSampleIndex++) {
    fLastOutput
      = (fAmountOfCurrent * *pfInput
       + fAmountOfLast * fLastOutput);
    *(pfOutput++) = *(pfInput++) - fLastOutput;
  }
  
  psFilter->m_fLastOutput = fLastOutput;
}

/*****************************************************************************/

/* Throw away a filter instance. Normally separate functions
   would have to be written for the different plugin types, however we
   can get away with a single function in this case. */
void 
cleanupSimpleFilter(LADSPA_Handle Instance) {
  free(Instance);
}

/*****************************************************************************/

LADSPA_Descriptor * g_psLPFDescriptor = NULL;
LADSPA_Descriptor * g_psHPFDescriptor = NULL;

/*****************************************************************************/

/* _init() is called automatically when the plugin library is first
   loaded. */
void 
_init() {

  char ** pcPortNames;
  LADSPA_PortDescriptor * piPortDescriptors;
  LADSPA_PortRangeHint * psPortRangeHints;
  
  g_psLPFDescriptor
    = (LADSPA_Descriptor *)malloc(sizeof(LADSPA_Descriptor));
  g_psHPFDescriptor 
    = (LADSPA_Descriptor *)malloc(sizeof(LADSPA_Descriptor));

  if (g_psLPFDescriptor != NULL) {
  
    g_psLPFDescriptor->UniqueID
      = 1041;
    g_psLPFDescriptor->Label
      = strdup("lpf");
    g_psLPFDescriptor->Properties
      = LADSPA_PROPERTY_HARD_RT_CAPABLE;
    g_psLPFDescriptor->Name 
      = strdup("Simple Low Pass Filter");
    g_psLPFDescriptor->Maker
      = strdup("Richard Furse (LADSPA example plugins)");
    g_psLPFDescriptor->Copyright
      = strdup("None");
    g_psLPFDescriptor->PortCount
      = 3;
    piPortDescriptors
      = (LADSPA_PortDescriptor *)calloc(3, sizeof(LADSPA_PortDescriptor));
    g_psLPFDescriptor->PortDescriptors
      = (const LADSPA_PortDescriptor *)piPortDescriptors;
    piPortDescriptors[SF_CUTOFF]
      = LADSPA_PORT_INPUT | LADSPA_PORT_CONTROL;
    piPortDescriptors[SF_INPUT]
      = LADSPA_PORT_INPUT | LADSPA_PORT_AUDIO;
    piPortDescriptors[SF_OUTPUT]
      = LADSPA_PORT_OUTPUT | LADSPA_PORT_AUDIO;
    pcPortNames
      = (char **)calloc(3, sizeof(char *));
    g_psLPFDescriptor->PortNames 
      = (const char **)pcPortNames;
    pcPortNames[SF_CUTOFF]
      = strdup("Cutoff Frequency (Hz)");
    pcPortNames[SF_INPUT]
      = strdup("Input");
    pcPortNames[SF_OUTPUT]
      = strdup("Output");
    psPortRangeHints = ((LADSPA_PortRangeHint *)
                  calloc(3, sizeof(LADSPA_PortRangeHint)));
    g_psLPFDescriptor->PortRangeHints
      = (const LADSPA_PortRangeHint *)psPortRangeHints;
    psPortRangeHints[SF_CUTOFF].HintDescriptor
      = (LADSPA_HINT_BOUNDED_BELOW 
       | LADSPA_HINT_BOUNDED_ABOVE
       | LADSPA_HINT_SAMPLE_RATE
       | LADSPA_HINT_LOGARITHMIC
       | LADSPA_HINT_DEFAULT_440);
    psPortRangeHints[SF_CUTOFF].LowerBound 
      = 0;
    psPortRangeHints[SF_CUTOFF].UpperBound
      = 0.5; /* Nyquist frequency (half the sample rate) */
    psPortRangeHints[SF_INPUT].HintDescriptor
      = 0;
    psPortRangeHints[SF_OUTPUT].HintDescriptor
      = 0;
    g_psLPFDescriptor->instantiate 
      = instantiateSimpleFilter;
    g_psLPFDescriptor->connect_port 
      = connectPortToSimpleFilter;
    g_psLPFDescriptor->activate
      = activateSimpleFilter;
    g_psLPFDescriptor->run
      = runSimpleLowPassFilter;
    g_psLPFDescriptor->run_adding
      = NULL;
    g_psLPFDescriptor->set_run_adding_gain
      = NULL;
    g_psLPFDescriptor->deactivate
      = NULL;
    g_psLPFDescriptor->cleanup
      = cleanupSimpleFilter;
  }
    
  if (g_psHPFDescriptor != NULL) {

    g_psHPFDescriptor->UniqueID
      = 1042;
    g_psHPFDescriptor->Label
      = strdup("hpf");
    g_psHPFDescriptor->Properties
      = LADSPA_PROPERTY_HARD_RT_CAPABLE;
    g_psHPFDescriptor->Name 
      = strdup("Simple High Pass Filter");
    g_psHPFDescriptor->Maker
      = strdup("Richard Furse (LADSPA example plugins)");
    g_psHPFDescriptor->Copyright
      = strdup("None");
    g_psHPFDescriptor->PortCount
      = 3;
    piPortDescriptors
      = (LADSPA_PortDescriptor *)calloc(3, sizeof(LADSPA_PortDescriptor));
    g_psHPFDescriptor->PortDescriptors
      = (const LADSPA_PortDescriptor *)piPortDescriptors;
    piPortDescriptors[SF_CUTOFF]
      = LADSPA_PORT_INPUT | LADSPA_PORT_CONTROL;
    piPortDescriptors[SF_INPUT]
      = LADSPA_PORT_INPUT | LADSPA_PORT_AUDIO;
    piPortDescriptors[SF_OUTPUT]
      = LADSPA_PORT_OUTPUT | LADSPA_PORT_AUDIO;
    pcPortNames
      = (char **)calloc(3, sizeof(char *));
    g_psHPFDescriptor->PortNames 
      = (const char **)pcPortNames;
    pcPortNames[SF_CUTOFF]
      = strdup("Cutoff Frequency (Hz)");
    pcPortNames[SF_INPUT]
      = strdup("Input");
    pcPortNames[SF_OUTPUT]
      = strdup("Output");
    psPortRangeHints = ((LADSPA_PortRangeHint *)
                  calloc(3, sizeof(LADSPA_PortRangeHint)));
    g_psHPFDescriptor->PortRangeHints
      = (const LADSPA_PortRangeHint *)psPortRangeHints;
    psPortRangeHints[SF_CUTOFF].HintDescriptor
      = (LADSPA_HINT_BOUNDED_BELOW 
       | LADSPA_HINT_BOUNDED_ABOVE
       | LADSPA_HINT_SAMPLE_RATE
       | LADSPA_HINT_LOGARITHMIC
       | LADSPA_HINT_DEFAULT_440);
    psPortRangeHints[SF_CUTOFF].LowerBound 
      = 0;
    psPortRangeHints[SF_CUTOFF].UpperBound
      = 0.5; /* Nyquist frequency (half the sample rate) */
    psPortRangeHints[SF_INPUT].HintDescriptor
      = 0;
    psPortRangeHints[SF_OUTPUT].HintDescriptor
      = 0;
    g_psHPFDescriptor->instantiate 
      = instantiateSimpleFilter;
    g_psHPFDescriptor->connect_port 
      = connectPortToSimpleFilter;
    g_psHPFDescriptor->activate
      = activateSimpleFilter;
    g_psHPFDescriptor->run
      = runSimpleHighPassFilter;
    g_psHPFDescriptor->run_adding
      = NULL;
    g_psHPFDescriptor->set_run_adding_gain
      = NULL;
    g_psHPFDescriptor->deactivate
      = NULL;
    g_psHPFDescriptor->cleanup
      = cleanupSimpleFilter;
  }
}
  
/*****************************************************************************/

void
deleteDescriptor(LADSPA_Descriptor * psDescriptor) {
  unsigned long lIndex;
  if (psDescriptor) {
    free((char *)psDescriptor->Label);
    free((char *)psDescriptor->Name);
    free((char *)psDescriptor->Maker);
    free((char *)psDescriptor->Copyright);
    free((LADSPA_PortDescriptor *)psDescriptor->PortDescriptors);
    for (lIndex = 0; lIndex < psDescriptor->PortCount; lIndex++)
      free((char *)(psDescriptor->PortNames[lIndex]));
    free((char **)psDescriptor->PortNames);
    free((LADSPA_PortRangeHint *)psDescriptor->PortRangeHints);
    free(psDescriptor);
  }
}

/*****************************************************************************/

/* _fini() is called automatically when the library is unloaded. */
void
_fini() {
  deleteDescriptor(g_psLPFDescriptor);
  deleteDescriptor(g_psHPFDescriptor);
}

/*****************************************************************************/

/* Return a descriptor of the requested plugin type. There are two
   plugin types available in this library. */
const LADSPA_Descriptor * 
ladspa_descriptor(unsigned long Index) {
  /* Return the requested descriptor or null if the index is out of
     range. */
  switch (Index) {
  case 0:
    return g_psLPFDescriptor;
  case 1:
    return g_psHPFDescriptor;
  default:
    return NULL;
  }
}

/*****************************************************************************/

/* EOF */

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