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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::dsp
27{
28
29 template <typename FloatType>
30 LookupTable<FloatType>::LookupTable()
31{
32 data.resize (1);
33}
34
35 template <typename FloatType>
36 LookupTable<FloatType>::LookupTable (const std::function<FloatType (size_t)>& functionToApproximate,
37 size_t numPointsToUse)
38{
39 initialise (functionToApproximate, numPointsToUse);
40}
41
42//==============================================================================
43 template <typename FloatType>
44 void LookupTable<FloatType>::initialise (const std::function<FloatType (size_t)>& functionToApproximate,
45 size_t numPointsToUse)
46{
47 data.resize (static_cast<int> (getRequiredBufferSize (numPointsToUse)));
48
49 for (size_t i = 0; i < numPointsToUse; ++i)
50 {
51 auto value = functionToApproximate (i);
52
53 jassert (! std::isnan (value));
54 jassert (! std::isinf (value));
55 // Make sure functionToApproximate returns a sensible value for the entire specified range.
56 // E.g., this won't work for zero: [] (size_t i) { return 1.0f / i; }
57
58 data.getReference (static_cast<int> (i)) = value;
59 }
60
61 prepare();
62}
63
64 template <typename FloatType>
65 void LookupTable<FloatType>::prepare() noexcept
66{
67 auto guardIndex = static_cast<int> (getGuardIndex());
68 data.getReference (guardIndex) = data.getUnchecked (guardIndex - 1);
69}
70
71 template <typename FloatType>
72 void LookupTableTransform<FloatType>::initialise (const std::function<FloatType (FloatType)>& functionToApproximate,
73 FloatType minInputValueToUse,
74 FloatType maxInputValueToUse,
75 size_t numPoints)
76{
77 jassert (maxInputValueToUse > minInputValueToUse);
78
79 minInputValue = minInputValueToUse;
80 maxInputValue = maxInputValueToUse;
81 scaler = FloatType (numPoints - 1) / (maxInputValueToUse - minInputValueToUse);
82 offset = -minInputValueToUse * scaler;
83
84 const auto initFn = [functionToApproximate, minInputValueToUse, maxInputValueToUse, numPoints] (size_t i)
85 {
86 return functionToApproximate (
87 jlimit (
88 minInputValueToUse, maxInputValueToUse,
89 jmap (FloatType (i), FloatType (0), FloatType (numPoints - 1), minInputValueToUse, maxInputValueToUse))
90 );
91 };
92
93 lookupTable.initialise (initFn, numPoints);
94}
95
96//==============================================================================
97 template <typename FloatType>
98 double LookupTableTransform<FloatType>::calculateMaxRelativeError (const std::function<FloatType (FloatType)>& functionToApproximate,
99 FloatType minInputValue,
100 FloatType maxInputValue,
101 size_t numPoints,
102 size_t numTestPoints)
103{
104 jassert (maxInputValue > minInputValue);
105
106 if (numTestPoints == 0)
107 numTestPoints = 100 * numPoints; // use default
108
109 LookupTableTransform transform (functionToApproximate, minInputValue, maxInputValue, numPoints);
110
111 double maxError = 0;
112
113 for (size_t i = 0; i < numTestPoints; ++i)
114 {
115 auto inputValue = jmap (FloatType (i), FloatType (0), FloatType (numTestPoints - 1), minInputValue, maxInputValue);
116 auto approximatedOutputValue = transform.processSample (inputValue);
117 auto referenceOutputValue = functionToApproximate (inputValue);
118
119 maxError = jmax (maxError, calculateRelativeDifference ((double) referenceOutputValue, (double) approximatedOutputValue));
120 }
121
122 return maxError;
123}
124
125//==============================================================================
126 template <typename FloatType>
127 double LookupTableTransform<FloatType>::calculateRelativeDifference (double x, double y) noexcept
128{
129 static const auto eps = std::numeric_limits<double>::min();
130
131 auto absX = std::abs (x);
132 auto absY = std::abs (y);
133 auto absDiff = std::abs (x - y);
134
135 if (absX < eps)
136 {
137 if (absY >= eps)
138 return absDiff / absY;
139
140 return absDiff; // return the absolute error if both numbers are too close to zero
141 }
142
143 return absDiff / std::min (absX, absY);
144}
145
146//==============================================================================
147 template class LookupTable<float>;
148 template class LookupTable<double>;
149
150 template class LookupTableTransform<float>;
151 template class LookupTableTransform<double>;
152
153} // namespace juce::dsp
juce::dsp::LookupTableTransform
Definition juce_LookupTable.h:173
juce::dsp::LookupTableTransform::initialise
void initialise(const std::function< FloatType(FloatType)> &functionToApproximate, FloatType minInputValueToUse, FloatType maxInputValueToUse, size_t numPoints)
Definition juce_LookupTable.cpp:72
juce::dsp::LookupTableTransform::processSample
FloatType processSample(FloatType value) const noexcept
Definition juce_LookupTable.h:251
juce::dsp::LookupTableTransform::calculateMaxRelativeError
static double calculateMaxRelativeError(const std::function< FloatType(FloatType)> &functionToApproximate, FloatType minInputValue, FloatType maxInputValue, size_t numPoints, size_t numTestPoints=0)
Definition juce_LookupTable.cpp:98
juce::dsp::LookupTable
Definition juce_LookupTable.h:51
juce::dsp::LookupTable::getUnchecked
FloatType getUnchecked(FloatType index) const noexcept
Definition juce_LookupTable.h:93
juce::dsp::LookupTable::initialise
void initialise(const std::function< FloatType(size_t)> &functionToApproximate, size_t numPointsToUse)
Definition juce_LookupTable.cpp:44
juce::dsp::LookupTable::LookupTable
LookupTable()
Definition juce_LookupTable.cpp:30