juce_LookupTable.h

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 /*
  ==============================================================================
 
   This file is part of the JUCE library.
   Copyright (c) 2022 - Raw Material Software Limited
 
   JUCE is an open source library subject to commercial or open-source
   licensing.
 
   By using JUCE, you agree to the terms of both the JUCE 7 End-User License
   Agreement and JUCE Privacy Policy.
 
   End User License Agreement: www.juce.com/juce-7-licence
   Privacy Policy: www.juce.com/juce-privacy-policy
 
   Or: You may also use this code under the terms of the GPL v3 (see
   www.gnu.org/licenses).
 
   JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
   EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
   DISCLAIMED.
 
  ==============================================================================
*/
 
namespace juce::dsp
{
 
template <typename FloatType>
class LookupTable
{
public:
    LookupTable();
 
    LookupTable (const std::function<FloatType (size_t)>& functionToApproximate, size_t numPointsToUse);
 
    void initialise (const std::function<FloatType (size_t)>& functionToApproximate, size_t numPointsToUse);
 
    //==============================================================================
    FloatType getUnchecked (FloatType index) const noexcept
    {
        jassert (isInitialised());  // Use the non-default constructor or call initialise() before first use
        jassert (isPositiveAndBelow (index, FloatType (getNumPoints())));
 
        auto i = truncatePositiveToUnsignedInt (index);
        auto f = index - FloatType (i);
        jassert (isPositiveAndBelow (f, FloatType (1)));
 
        auto x0 = data.getUnchecked (static_cast<int> (i));
        auto x1 = data.getUnchecked (static_cast<int> (i + 1));
 
        return jmap (f, x0, x1);
    }
 
    //==============================================================================
    FloatType get (FloatType index) const noexcept
    {
        if (index >= (FloatType) getNumPoints())
            index = static_cast<FloatType> (getGuardIndex());
        else if (index < 0)
            index = {};
 
        return getUnchecked (index);
    }
 
    //==============================================================================
    FloatType operator[] (FloatType index) const noexcept       { return getUnchecked (index); }
 
    size_t getNumPoints() const noexcept                        { return static_cast<size_t> (data.size()) - 1; }
 
    bool isInitialised() const noexcept                         { return data.size() > 1; }
 
private:
    //==============================================================================
    Array<FloatType> data;
 
    void prepare() noexcept;
    static size_t getRequiredBufferSize (size_t numPointsToUse) noexcept { return numPointsToUse + 1; }
    size_t getGuardIndex() const noexcept                                { return getRequiredBufferSize (getNumPoints()) - 1; }
 
    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (LookupTable)
};
 
 
//==============================================================================
template <typename FloatType>
class LookupTableTransform
{
public:
    //==============================================================================
    LookupTableTransform() = default;
 
    //==============================================================================
    LookupTableTransform (const std::function<FloatType (FloatType)>& functionToApproximate,
                          FloatType minInputValueToUse,
                          FloatType maxInputValueToUse,
                          size_t numPoints)
    {
        initialise (functionToApproximate, minInputValueToUse, maxInputValueToUse, numPoints);
    }
 
    //==============================================================================
    void initialise (const std::function<FloatType (FloatType)>& functionToApproximate,
                     FloatType minInputValueToUse,
                     FloatType maxInputValueToUse,
                     size_t numPoints);
 
    //==============================================================================
    FloatType processSampleUnchecked (FloatType value) const noexcept
    {
        jassert (value >= minInputValue && value <= maxInputValue);
        return lookupTable[scaler * value + offset];
    }
 
    //==============================================================================
    FloatType processSample (FloatType value) const noexcept
    {
        auto index = scaler * jlimit (minInputValue, maxInputValue, value) + offset;
        jassert (isPositiveAndBelow (index, FloatType (lookupTable.getNumPoints())));
 
        return lookupTable[index];
    }
 
    //==============================================================================
    FloatType operator[] (FloatType index) const noexcept       { return processSampleUnchecked (index); }
 
    FloatType operator() (FloatType index) const noexcept       { return processSample (index); }
 
    //==============================================================================
    void processUnchecked (const FloatType* input, FloatType* output, size_t numSamples) const noexcept
    {
        for (size_t i = 0; i < numSamples; ++i)
            output[i] = processSampleUnchecked (input[i]);
    }
 
    //==============================================================================
    void process (const FloatType* input, FloatType* output, size_t numSamples) const noexcept
    {
        for (size_t i = 0; i < numSamples; ++i)
            output[i] = processSample (input[i]);
    }
 
    //==============================================================================
    static double calculateMaxRelativeError (const std::function<FloatType (FloatType)>& functionToApproximate,
                                             FloatType minInputValue,
                                             FloatType maxInputValue,
                                             size_t numPoints,
                                             size_t numTestPoints = 0);
private:
    //==============================================================================
    static double calculateRelativeDifference (double, double) noexcept;
 
    //==============================================================================
    LookupTable<FloatType> lookupTable;
 
    FloatType minInputValue, maxInputValue;
    FloatType scaler, offset;
 
    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (LookupTableTransform)
};
 
} // namespace juce::dsp