OpenShot Audio Library | OpenShotAudio  0.3.0
juce_LookupTable.cpp
1 /*
2  ==============================================================================
3 
4  This file is part of the JUCE library.
5  Copyright (c) 2017 - ROLI Ltd.
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 5 End-User License
11  Agreement and JUCE 5 Privacy Policy (both updated and effective as of the
12  27th April 2017).
13 
14  End User License Agreement: www.juce.com/juce-5-licence
15  Privacy Policy: www.juce.com/juce-5-privacy-policy
16 
17  Or: You may also use this code under the terms of the GPL v3 (see
18  www.gnu.org/licenses).
19 
20  JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
21  EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
22  DISCLAIMED.
23 
24  ==============================================================================
25 */
26 
27 namespace juce
28 {
29 namespace dsp
30 {
31 
32 template <typename FloatType>
34 {
35  data.resize (1);
36 }
37 
38 template <typename FloatType>
39 LookupTable<FloatType>::LookupTable (const std::function<FloatType(size_t)>& functionToApproximate,
40  size_t numPointsToUse)
41 {
42  initialise (functionToApproximate, numPointsToUse);
43 }
44 
45 //==============================================================================
46 template <typename FloatType>
47 void LookupTable<FloatType>::initialise (const std::function<FloatType(size_t)>& functionToApproximate,
48  size_t numPointsToUse)
49 {
50  data.resize (static_cast<int> (getRequiredBufferSize (numPointsToUse)));
51 
52  for (size_t i = 0; i < numPointsToUse; ++i)
53  {
54  auto value = functionToApproximate (i);
55 
56  jassert (! std::isnan (value));
57  jassert (! std::isinf (value));
58  // Make sure functionToApproximate returns a sensible value for the entire specified range.
59  // E.g., this won't work for zero: [] (size_t i) { return 1.0f / i; }
60 
61  data.getReference (static_cast<int> (i)) = value;
62  }
63 
64  prepare();
65 }
66 
67 template <typename FloatType>
68 void LookupTable<FloatType>::prepare() noexcept
69 {
70  auto guardIndex = static_cast<int> (getGuardIndex());
71  data.getReference (guardIndex) = data.getUnchecked (guardIndex - 1);
72 }
73 
74 template <typename FloatType>
75 void LookupTableTransform<FloatType>::initialise (const std::function<FloatType(FloatType)>& functionToApproximate,
76  FloatType minInputValueToUse,
77  FloatType maxInputValueToUse,
78  size_t numPoints)
79 {
80  jassert (maxInputValueToUse > minInputValueToUse);
81 
82  minInputValue = minInputValueToUse;
83  maxInputValue = maxInputValueToUse;
84  scaler = FloatType (numPoints - 1) / (maxInputValueToUse - minInputValueToUse);
85  offset = -minInputValueToUse * scaler;
86 
87  const auto initFn = [functionToApproximate, minInputValueToUse, maxInputValueToUse, numPoints] (size_t i)
88  {
89  return functionToApproximate (
90  jlimit (
91  minInputValueToUse, maxInputValueToUse,
92  jmap (FloatType (i), FloatType (0), FloatType (numPoints - 1), minInputValueToUse, maxInputValueToUse))
93  );
94  };
95 
96  lookupTable.initialise (initFn, numPoints);
97 }
98 
99 //==============================================================================
100 template <typename FloatType>
101 double LookupTableTransform<FloatType>::calculateMaxRelativeError (const std::function<FloatType(FloatType)>& functionToApproximate,
102  FloatType minInputValue,
103  FloatType maxInputValue,
104  size_t numPoints,
105  size_t numTestPoints)
106 {
107  jassert (maxInputValue > minInputValue);
108 
109  if (numTestPoints == 0)
110  numTestPoints = 100 * numPoints; // use default
111 
112  LookupTableTransform transform (functionToApproximate, minInputValue, maxInputValue, numPoints);
113 
114  double maxError = 0;
115 
116  for (size_t i = 0; i < numTestPoints; ++i)
117  {
118  auto inputValue = jmap (FloatType (i), FloatType (0), FloatType (numTestPoints - 1), minInputValue, maxInputValue);
119  auto approximatedOutputValue = transform.processSample (inputValue);
120  auto referenceOutputValue = functionToApproximate (inputValue);
121 
122  maxError = jmax (maxError, calculateRelativeDifference ((double) referenceOutputValue, (double) approximatedOutputValue));
123  }
124 
125  return maxError;
126 }
127 
128 //==============================================================================
129 template <typename FloatType>
130 double LookupTableTransform<FloatType>::calculateRelativeDifference (double x, double y) noexcept
131 {
132  static const auto eps = std::numeric_limits<double>::min();
133 
134  auto absX = std::abs (x);
135  auto absY = std::abs (y);
136  auto absDiff = std::abs (x - y);
137 
138  if (absX < eps)
139  {
140  if (absY >= eps)
141  return absDiff / absY;
142 
143  return absDiff; // return the absolute error if both numbers are too close to zero
144  }
145 
146  return absDiff / std::min (absX, absY);
147 }
148 
149 //==============================================================================
150 template class LookupTable<float>;
151 template class LookupTable<double>;
152 
153 template class LookupTableTransform<float>;
154 template class LookupTableTransform<double>;
155 
156 } // namespace dsp
157 } // namespace juce
void initialise(const std::function< FloatType(FloatType)> &functionToApproximate, FloatType minInputValueToUse, FloatType maxInputValueToUse, size_t numPoints)
void initialise(const std::function< FloatType(size_t)> &functionToApproximate, size_t numPointsToUse)
FloatType processSample(FloatType value) const noexcept
FloatType getUnchecked(FloatType index) const noexcept
static double calculateMaxRelativeError(const std::function< FloatType(FloatType)> &functionToApproximate, FloatType minInputValue, FloatType maxInputValue, size_t numPoints, size_t numTestPoints=0)