amath  1.8.5
Simple command line calculator
log2i.c
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1 /*-
2  * Copyright (c) 2014-2018 Carsten Sonne Larsen <cs@innolan.net>
3  * All rights reserved.
4  *
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9  * notice, this list of conditions and the following disclaimer.
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11  * notice, this list of conditions and the following disclaimer in the
12  * documentation and/or other materials provided with the distribution.
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28  * The original source code can be obtained from:
29  * http://graphics.stanford.edu/~seander/bithacks.html
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31  */
32 
33 #include "amath.h"
34 
35 uint32_t log2i(uint32_t val)
36 {
37  static const char logTable[256] =
38  {
39  0, 0, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3,
40  4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
41  5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
42  5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
43  6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
44  6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
45  6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
46  6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
47  7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
48  7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
49  7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
50  7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
51  7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
52  7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
53  7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
54  7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7};
55 
56  uint32_t temp;
57 
58  temp = val >> 24;
59  if (temp)
60  return 24 + logTable[temp];
61 
62  temp = val >> 16;
63  if (temp)
64  return 16 + logTable[temp];
65 
66  temp = val >> 8;
67  if (temp)
68  return 8 + logTable[temp];
69 
70  return logTable[val];
71 }
uint32_t log2i(uint32_t val)
Definition: log2i.c:35