source/modules/juce_dsp/maths/juce_LookupTable.cpp

   1 /*
   2   ==============================================================================
   3
   4    This file is part of the JUCE library.
   5    Copyright (c) 2022 - Raw Material Software Limited
   6
   7    JUCE is an open source library subject to commercial or open-source
   8    licensing.
   9
  10    By using JUCE, you agree to the terms of both the JUCE 7 End-User License
  11    Agreement and JUCE Privacy Policy.
  12
  13    End User License Agreement: www.juce.com/juce-7-licence
  14    Privacy Policy: www.juce.com/juce-privacy-policy
  15
  16    Or: You may also use this code under the terms of the GPL v3 (see
  17    www.gnu.org/licenses).
  18
  19    JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
  20    EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
  21    DISCLAIMED.
  22
  23   ==============================================================================
  24 */
  25
  26 namespace juce
  27 {
  28 namespace dsp
  29 {
  30
  31 template <typename FloatType>
  32 LookupTable<FloatType>::LookupTable()
  33 {
  34     data.resize (1);
  35 }
  36
  37 template <typename FloatType>
  38 LookupTable<FloatType>::LookupTable (const std::function<FloatType (size_t)>& functionToApproximate,
  39                                      size_t numPointsToUse)
  40 {
  41     initialise (functionToApproximate, numPointsToUse);
  42 }
  43
  44 //==============================================================================
  45 template <typename FloatType>
  46 void LookupTable<FloatType>::initialise (const std::function<FloatType (size_t)>& functionToApproximate,
  47                                          size_t numPointsToUse)
  48 {
  49     data.resize (static_cast<int> (getRequiredBufferSize (numPointsToUse)));
  50
  51     for (size_t i = 0; i < numPointsToUse; ++i)
  52     {
  53         auto value = functionToApproximate (i);
  54
  55         jassert (! std::isnan (value));
  56         jassert (! std::isinf (value));
  57         // Make sure functionToApproximate returns a sensible value for the entire specified range.
  58         // E.g., this won't work for zero:  [] (size_t i) { return 1.0f / i; }
  59
  60         data.getReference (static_cast<int> (i)) = value;
  61     }
  62
  63     prepare();
  64 }
  65
  66 template <typename FloatType>
  67 void LookupTable<FloatType>::prepare() noexcept
  68 {
  69     auto guardIndex = static_cast<int> (getGuardIndex());
  70     data.getReference (guardIndex) = data.getUnchecked (guardIndex - 1);
  71 }
  72
  73 template <typename FloatType>
  74 void LookupTableTransform<FloatType>::initialise (const std::function<FloatType (FloatType)>& functionToApproximate,
  75                                                   FloatType minInputValueToUse,
  76                                                   FloatType maxInputValueToUse,
  77                                                   size_t numPoints)
  78 {
  79     jassert (maxInputValueToUse > minInputValueToUse);
  80
  81     minInputValue = minInputValueToUse;
  82     maxInputValue = maxInputValueToUse;
  83     scaler = FloatType (numPoints - 1) / (maxInputValueToUse - minInputValueToUse);
  84     offset = -minInputValueToUse * scaler;
  85
  86     const auto initFn = [functionToApproximate, minInputValueToUse, maxInputValueToUse, numPoints] (size_t i)
  87     {
  88         return functionToApproximate (
  89             jlimit (
  90                 minInputValueToUse, maxInputValueToUse,
  91                 jmap (FloatType (i), FloatType (0), FloatType (numPoints - 1), minInputValueToUse, maxInputValueToUse))
  92             );
  93     };
  94
  95     lookupTable.initialise (initFn, numPoints);
  96 }
  97
  98 //==============================================================================
  99 template <typename FloatType>
 100 double LookupTableTransform<FloatType>::calculateMaxRelativeError (const std::function<FloatType (FloatType)>& functionToApproximate,
 101                                                                    FloatType minInputValue,
 102                                                                    FloatType maxInputValue,
 103                                                                    size_t numPoints,
 104                                                                    size_t numTestPoints)
 105 {
 106     jassert (maxInputValue > minInputValue);
 107
 108     if (numTestPoints == 0)
 109         numTestPoints = 100 * numPoints;    // use default
 110
 111     LookupTableTransform transform (functionToApproximate, minInputValue, maxInputValue, numPoints);
 112
 113     double maxError = 0;
 114
 115     for (size_t i = 0; i < numTestPoints; ++i)
 116     {
 117         auto inputValue = jmap (FloatType (i), FloatType (0), FloatType (numTestPoints - 1), minInputValue, maxInputValue);
 118         auto approximatedOutputValue = transform.processSample (inputValue);
 119         auto referenceOutputValue = functionToApproximate (inputValue);
 120
 121         maxError = jmax (maxError, calculateRelativeDifference ((double) referenceOutputValue, (double) approximatedOutputValue));
 122     }
 123
 124     return maxError;
 125 }
 126
 127 //==============================================================================
 128 template <typename FloatType>
 129 double LookupTableTransform<FloatType>::calculateRelativeDifference (double x, double y) noexcept
 130 {
 131     static const auto eps = std::numeric_limits<double>::min();
 132
 133     auto absX = std::abs (x);
 134     auto absY = std::abs (y);
 135     auto absDiff = std::abs (x - y);
 136
 137     if (absX < eps)
 138     {
 139         if (absY >= eps)
 140             return absDiff / absY;
 141
 142         return absDiff;    // return the absolute error if both numbers are too close to zero
 143     }
 144
 145     return absDiff / std::min (absX, absY);
 146 }
 147
 148 //==============================================================================
 149 template class LookupTable<float>;
 150 template class LookupTable<double>;
 151
 152 template class LookupTableTransform<float>;
 153 template class LookupTableTransform<double>;
 154
 155 } // namespace dsp
 156 } // namespace juce