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toFloat.cpp
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1 
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34 
35 
36 
37 
38 //---------------------------------------------------------------------------
39 //
40 // toFloat
41 //
42 // A program to generate the lookup table for half-to-float
43 // conversion needed by class half.
44 // The program loops over all 65536 possible half numbers,
45 // converts each of them to a float, and prints the result.
46 //
47 //---------------------------------------------------------------------------
48 
49 
50 #include <iostream>
51 #include <iomanip>
52 
53 using namespace std;
54 
55 //---------------------------------------------------
56 // Interpret an unsigned short bit pattern as a half,
57 // and convert that half to the corresponding float's
58 // bit pattern.
59 //---------------------------------------------------
60 
61 unsigned int
62 halfToFloat (unsigned short y)
63 {
64 
65  int s = (y >> 15) & 0x00000001;
66  int e = (y >> 10) & 0x0000001f;
67  int m = y & 0x000003ff;
68 
69  if (e == 0)
70  {
71  if (m == 0)
72  {
73  //
74  // Plus or minus zero
75  //
76  // cppcheck-suppress integerOverflow
77  return s << 31;
78  }
79  else
80  {
81  //
82  // Denormalized number -- renormalize it
83  //
84 
85  while (!(m & 0x00000400))
86  {
87  m <<= 1;
88  e -= 1;
89  }
90 
91  e += 1;
92  m &= ~0x00000400;
93  }
94  }
95  else if (e == 31)
96  {
97  if (m == 0)
98  {
99  //
100  // Positive or negative infinity
101  //
102  // cppcheck-suppress integerOverflow
103  return (s << 31) | 0x7f800000;
104  }
105  else
106  {
107  //
108  // Nan -- preserve sign and significand bits
109  //
110  // cppcheck-suppress integerOverflow
111  return (s << 31) | 0x7f800000 | (m << 13);
112  }
113  }
114 
115  //
116  // Normalized number
117  //
118 
119  e = e + (127 - 15);
120  m = m << 13;
121 
122  //
123  // Assemble s, e and m.
124  //
125  // cppcheck-suppress integerOverflow
126  return (s << 31) | (e << 23) | m;
127 }
128 
129 
130 //---------------------------------------------
131 // Main - prints the half-to-float lookup table
132 //---------------------------------------------
133 
134 int
136 {
137  cout.precision (9);
138  cout.setf (ios_base::hex, ios_base::basefield);
139 
140  cout << "//\n"
141  "// This is an automatically generated file.\n"
142  "// Do not edit.\n"
143  "//\n\n";
144 
145  cout << "{\n ";
146 
147  const int iMax = (1 << 16);
148 
149  for (int i = 0; i < iMax; i++)
150  {
151  cout << "{0x" << setfill ('0') << setw (8) << halfToFloat (i) << "}, ";
152 
153  if (i % 4 == 3)
154  {
155  cout << "\n";
156 
157  if (i < iMax - 1)
158  cout << " ";
159  }
160  }
161 
162  cout << "};\n";
163  return 0;
164 }