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+/* Copyright 2012 Dietrich Epp <depp@zdome.net> */
+#pragma once
+
+#include <array>
+
+/*
+ Parameters for the filter generator.
+
+ Filter generation goes through two stages.
+
+ 1. In the first stage, the resampling parameters are used to create
+ a filter specification.  The filter specification consists of
+ normalized frequencies for the pass band, stop band, and stop band
+ attenuation.  This stage uses simple logic to create a filter
+ specification that "makes sense" for any input.  It relaxes the
+ filter specification for ultrasonic (inaudible) frequencies and
+ ensures that enough of the input signal passes through.
+
+ 2. In the second stage, an FIR filter is generated that fits the
+ filter specified by the first stage.
+
+ Normally, for resampling, you will specify QUALITY, INRATE, and
+ OUTRATE.  A filter specification for the conversion will be
+ automatically generated with the given subjective quality level.
+
+ If you are a signal-processing guru, you can create the filter
+ specification directly by setting FPASS, FSTOP, and ATTEN.
+ */
+enum lfr_param_t {
+	/* High level filter parameters.  These are typi*cally the only
+		parameters you will need to set. */
+
+	/* Filter quality, default 8.  An integer between 0 and 10 which
+		determines the default values for other para*meters.  */
+	LFR_PARAM_QUALITY,
+
+	/* Input sample rate, in Hz.  The default is -1, which creates a
+		generic filter.  */
+	LFR_PARAM_INRATE,
+
+	 /* Output sample rate.  If the input sample rate is specified,
+		then this is measured in Hz.  Otherwise, if *the input rate is
+		-1, then this value is relative to the input sample rate (so
+		you would use 0.5 for downsampling by a factor of two).
+		Defaults to the same value as the input sample rate, which
+		creates a filter which can be used for upsampling at any ratio.
+		Note that increasing the output rate above the input rate has
+		no effect, all upsampling filters for a given input frequency
+		are identical.  */
+	 LFR_PARAM_OUTRATE,
+
+	 /*
+		Medium level filter parameters.  These parame*ters affect how the
+		filter specification is generated from the input and output
+		sample rates.  Most of these parameters have default values
+		which depend on the QUALITY setting.
+		*/
+
+	 /* The width of the filter transition band, as a fraction of the
+		input sample rate.  This value will be enlar*ged to extend the
+		transition band to MAXFREQ and will be narrowed to extend the
+		pass band to MINBW.  The default value depends on the QUALITY
+		setting, and gets narrower as QUALITY increases.  */
+	 LFR_PARAM_FTRANSITION,
+
+	 /* Maximum audible frequency.  The pass band will be narrowed to
+		fit within the range of audible frequencies.*  Default value is
+		20 kHz if the input frequency is set, otherwise this parameter
+		is unused.  If you want to preserve ultrasonic frequencies,
+		disable this parameter by setting it to -1.  This is disabled
+		by default at absurd quality settings (9 and 10).  */
+	 LFR_PARAM_MAXFREQ,
+
+	 /* A flag which allows aliasing noise as long as it is above
+		MAXFREQ.  This flag improves the subjective *quality of
+		low-quality filters by increasing their bandwidth, but causes
+		problems for high-quality filters by increasing noise.  Default
+		value depends on QUALITY setting, and is set for low QUALITY
+		values.  Has no effect if MAXFREQ is disabled.  */
+	 LFR_PARAM_LOOSE,
+
+	 /* Minimum size of pass band, as a fraction of the output
+		bandwidth.  This prevents the filter designe*r from filtering
+		out the entire signal, which can happen when downsampling by a
+		large enough ratio.  The default value is 0.5 at low quality
+		settings, and higher at high quality settings.  The filter size
+		can increase dramatically as this number approaches 1.0.  */
+	 LFR_PARAM_MINFPASS,
+
+	 /*
+		Filter specification.  These parameters are n*ormally generated
+		from the higher level parameters.  If the filter specification
+		is set, then the higher level parameters will all be ignored.
+		*/
+
+	 /* The end of the pass band, as a fraction of the input sample
+		rate.  Normally, the filter designer chooses* this value.  */
+	 LFR_PARAM_FPASS,
+
+	 /* The start of the stop band, as a fraction of the input sample
+		rate.  Normally, the filter designer chooses* this value.  */
+	 LFR_PARAM_FSTOP,
+
+	 /* Desired stop band attenuation, in dB.  Larger numbers are
+		increase filter quality.  Default value depe*nds on the QUALITY
+		setting.  */
+	LFR_PARAM_ATTEN,
+
+	LFR_PARAM_COUNT
+};
+
+class lfr_param {
+	/*
+		Bit set of which parameters were set by the user.
+	*/
+	unsigned set{0};
+
+	/*
+		Set to 1 if the derived parameters are up to date.
+	*/
+	int current{0};
+
+public:
+	/*
+		Parameter values.
+	*/
+	std::array<double, LFR_PARAM_COUNT> param;
+
+	void calculate();
+	void seti(lfr_param_t pname, int value);
+	void setf(lfr_param_t pname, double value);
+	void geti(lfr_param_t pname, int* value);
+	void getf(lfr_param_t pname, double* value);
+};
+