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halfFunction.h
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1 
2 //
3 // Copyright (c) 2002, Industrial Light & Magic, a division of Lucas
4 // Digital Ltd. LLC
5 //
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34 
35 // Primary authors:
36 // Florian Kainz <kainz@ilm.com>
37 // Rod Bogart <rgb@ilm.com>
38 
39 
40 //---------------------------------------------------------------------------
41 //
42 // halfFunction<T> -- a class for fast evaluation
43 // of half --> T functions
44 //
45 // The constructor for a halfFunction object,
46 //
47 // halfFunction (function,
48 // domainMin, domainMax,
49 // defaultValue,
50 // posInfValue, negInfValue,
51 // nanValue);
52 //
53 // evaluates the function for all finite half values in the interval
54 // [domainMin, domainMax], and stores the results in a lookup table.
55 // For finite half values that are not in [domainMin, domainMax], the
56 // constructor stores defaultValue in the table. For positive infinity,
57 // negative infinity and NANs, posInfValue, negInfValue and nanValue
58 // are stored in the table.
59 //
60 // The tabulated function can then be evaluated quickly for arbitrary
61 // half values by calling the the halfFunction object's operator()
62 // method.
63 //
64 // Example:
65 //
66 // #include <math.h>
67 // #include <halfFunction.h>
68 //
69 // halfFunction<half> hsin (sin);
70 //
71 // halfFunction<half> hsqrt (sqrt, // function
72 // 0, HALF_MAX, // domain
73 // half::qNan(), // sqrt(x) for x < 0
74 // half::posInf(), // sqrt(+inf)
75 // half::qNan(), // sqrt(-inf)
76 // half::qNan()); // sqrt(nan)
77 //
78 // half x = hsin (1);
79 // half y = hsqrt (3.5);
80 //
81 //---------------------------------------------------------------------------
82 
83 #ifndef _HALF_FUNCTION_H_
84 #define _HALF_FUNCTION_H_
85 
86 #include <float.h>
87 #include "half.h"
88 
89 
90 template <class T>
92 {
93  public:
94 
95  //------------
96  // Constructor
97  //------------
98 
99  template <class Function>
100  halfFunction (Function f,
101  half domainMin = -HALF_MAX,
102  half domainMax = HALF_MAX,
103  T defaultValue = 0,
104  T posInfValue = 0,
105  T negInfValue = 0,
106  T nanValue = 0);
107 
108  //-----------
109  // Evaluation
110  //-----------
111 
112  T operator () (half x) const;
113 
114  private:
115 
116  T _lut[1 << 16];
117 };
118 
119 
120 //---------------
121 // Implementation
122 //---------------
123 
124 template <class T>
125 template <class Function>
127  half domainMin,
128  half domainMax,
129  T defaultValue,
130  T posInfValue,
131  T negInfValue,
132  T nanValue)
133 {
134  for (int i = 0; i < (1 << 16); i++)
135  {
136  half x;
137  x.setBits (i);
138 
139  if (x.isNan())
140  _lut[i] = nanValue;
141  else if (x.isInfinity())
142  _lut[i] = x.isNegative()? negInfValue: posInfValue;
143  else if (x < domainMin || x > domainMax)
144  _lut[i] = defaultValue;
145  else
146  _lut[i] = f (x);
147  }
148 }
149 
150 
151 template <class T>
152 inline T
154 {
155  return _lut[x.bits()];
156 }
157 
158 
159 #endif