ATLAS Offline Software
BitPacker.icc
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1 /*
2  Copyright (C) 2002-2017 CERN for the benefit of the ATLAS collaboration
3 */
4 
5 // $Id$
6 /**
7  * @file CxxUtils/BitPacker.icc
8  * @author scott snyder <snyder@bnl.gov>
9  * @date Nov, 2014
10  * @brief Helper to pack a set of values bitwise into a stream.
11  */
12 
13 
14 namespace CxxUtils {
15 
16 
17 /**
18  * @brief Constructor.
19  * @param nbits Number of bits per item to use in the packed representation.
20  * @param stream Output stream object.
21  */
22 template <class STREAM>
23 inline
24 BitPacker<STREAM>::BitPacker (uint8_t nbits, STREAM& stream)
25  : m_buf(0),
26  m_nbuf(0),
27  m_nbits(nbits),
28  m_stream (stream)
29 {
30  assert (m_nbits > 0 && m_nbits <= 32);
31 }
32 
33 
34 /**
35  * @brief Destructor.
36  *
37  * This may flush buffered data to the output stream.
38  */
39 template <class STREAM>
40 inline
41 BitPacker<STREAM>::~BitPacker()
42 {
43  if (m_nbuf > 0)
44  m_stream << m_buf;
45 }
46 
47 
48 /**
49  * @brief Pack one value to the stream.
50  * @param x The value to pack.
51  * The upper bits should all be clear.
52  */
53 template <class STREAM>
54 inline
55 void BitPacker<STREAM>::pack (uint32_t dat)
56 {
57  const uint8_t totbits = 8*sizeof(m_buf);
58 
59  m_buf |= (dat << m_nbuf);
60  m_nbuf += m_nbits;
61  if (m_nbuf >= totbits) {
62  m_stream << m_buf;
63  m_nbuf -= totbits;
64  if (m_nbuf == 0)
65  m_buf = 0;
66  else
67  m_buf = dat >> (m_nbits - m_nbuf);
68  }
69 }
70 
71 
72 /**
73  * @brief Constructor.
74  * @param stream Output stream object.
75  */
76 template <class STREAM>
77 inline
78 BitPacker8<STREAM>::BitPacker8 (STREAM& stream)
79  : m_buf(0),
80  m_nbuf(0),
81  m_stream (stream)
82 {
83 }
84 
85 
86 /**
87  * @brief Constructor.
88  * @param nbits Must be 8.
89  * @param stream Output stream object.
90  */
91 template <class STREAM>
92 inline
93 BitPacker8<STREAM>::BitPacker8 (uint8_t /*nbits*/, STREAM& stream)
94  : m_buf(0),
95  m_nbuf(0),
96  m_stream (stream)
97 {
98 }
99 
100 
101 /**
102  * @brief Destructor.
103  *
104  * This may flush buffered data to the output stream.
105  */
106 template <class STREAM>
107 inline
108 BitPacker8<STREAM>::~BitPacker8()
109 {
110  if (m_nbuf > 0)
111  m_stream << m_buf;
112 }
113 
114 
115 /**
116  * @brief Pack one value to the stream.
117  * @param x The value to pack.
118  * The upper bits should all be clear.
119  */
120 template <class STREAM>
121 inline
122 void BitPacker8<STREAM>::pack (uint32_t dat)
123 {
124  m_buf |= (dat << m_nbuf);
125  m_nbuf += 8;
126  if (m_nbuf == 32) {
127  m_stream << m_buf;
128  m_buf = 0;
129  m_nbuf = 0;
130  }
131 }
132 
133 
134 /**
135  * @brief Constructor.
136  * @param stream Output stream object.
137  */
138 template <class STREAM>
139 inline
140 BitPacker16<STREAM>::BitPacker16 (STREAM& stream)
141  : m_buf(0),
142  m_nbuf(0),
143  m_stream (stream)
144 {
145 }
146 
147 
148 /**
149  * @brief Constructor.
150  * @param nbits Must be 16.
151  * @param stream Output stream object.
152  */
153 template <class STREAM>
154 inline
155 BitPacker16<STREAM>::BitPacker16 (uint8_t /*nbits*/, STREAM& stream)
156  : m_buf(0),
157  m_nbuf(0),
158  m_stream (stream)
159 {
160 }
161 
162 
163 /**
164  * @brief Destructor.
165  *
166  * This may flush buffered data to the output stream.
167  */
168 template <class STREAM>
169 inline
170 BitPacker16<STREAM>::~BitPacker16()
171 {
172  if (m_nbuf > 0)
173  m_stream << m_buf;
174 }
175 
176 
177 /**
178  * @brief Pack one value to the stream.
179  * @param x The value to pack.
180  * The upper bits should all be clear.
181  */
182 template <class STREAM>
183 inline
184 void BitPacker16<STREAM>::pack (uint32_t dat)
185 {
186  m_buf |= (dat << m_nbuf);
187  m_nbuf += 16;
188  if (m_nbuf == 32) {
189  m_stream << m_buf;
190  m_buf = 0;
191  m_nbuf = 0;
192  }
193 }
194 
195 
196 } // namespace CxxUtils
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