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eLut.cpp
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1 
2 //
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4 // Digital Ltd. LLC
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34 
35 
36 
37 #include <iostream>
38 #include <iomanip>
39 
40 using namespace std;
41 
42 //-----------------------------------------------------
43 // Compute a lookup table for float-to-half conversion.
44 //
45 // When indexed with the combined sign and exponent of
46 // a float, the table either returns the combined sign
47 // and exponent of the corresponding half, or zero if
48 // the corresponding half may not be normalized (zero,
49 // denormalized, overflow).
50 //-----------------------------------------------------
51 
52 void
53 initELut (unsigned short eLut[])
54 {
55  for (int i = 0; i < 0x100; i++)
56  {
57  int e = (i & 0x0ff) - (127 - 15);
58 
59  if (e <= 0 || e >= 30)
60  {
61  //
62  // Special case
63  //
64 
65  eLut[i] = 0;
66  eLut[i | 0x100] = 0;
67  }
68  else
69  {
70  //
71  // Common case - normalized half, no exponent overflow possible
72  //
73 
74  eLut[i] = (e << 10);
75  eLut[i | 0x100] = ((e << 10) | 0x8000);
76  }
77  }
78 }
79 
80 
81 //------------------------------------------------------------
82 // Main - prints the sign-and-exponent conversion lookup table
83 //------------------------------------------------------------
84 
85 int
86 main ()
87 {
88  const int tableSize = 1 << 9;
89  unsigned short eLut[tableSize];
90  initELut (eLut);
91 
92  cout << "//\n"
93  "// This is an automatically generated file.\n"
94  "// Do not edit.\n"
95  "//\n\n";
96 
97  cout << "{\n ";
98 
99  for (int i = 0; i < tableSize; i++)
100  {
101  cout << setw (5) << eLut[i] << ", ";
102 
103  if (i % 8 == 7)
104  {
105  cout << "\n";
106 
107  if (i < tableSize - 1)
108  cout << " ";
109  }
110  }
111 
112  cout << "};\n";
113  return 0;
114 }