2 This file is a part of libcds - Concurrent Data Structures library
4 (C) Copyright Maxim Khizhinsky (libcds.dev@gmail.com) 2006-2016
6 Source code repo: http://github.com/khizmax/libcds/
7 Download: http://sourceforge.net/projects/libcds/files/
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10 modification, are permitted provided that the following conditions are met:
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13 list of conditions and the following disclaimer.
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16 this list of conditions and the following disclaimer in the documentation
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31 #ifndef CDSLIB_ALGO_SPLIT_BITSTRING_H
32 #define CDSLIB_ALGO_SPLIT_BITSTRING_H
34 #include <cds/algo/base.h>
36 namespace cds { namespace algo {
38 /// Cuts a bit sequence from fixed-size bit-string
40 The splitter can be used as iterator over bit-string.
41 Each call of \p cut() or \p safe_cut() cuts the bit count specified
42 and keeps the position inside bit-string for the next call.
44 The splitter stores a const reference to bit-string, not a copy.
45 The maximum count of bits that can be cut in a single call is <tt> sizeof(UInt) * 8 </tt>
47 template <typename BitString, typename UInt = typename std::conditional< sizeof(BitString) % sizeof(size_t) == 0, size_t, unsigned >::type >
51 typedef BitString bitstring; ///< Bit-string type
52 typedef UInt uint_type; ///< Bit-string portion type
55 static CDS_CONSTEXPR size_t const c_nHashSize = (sizeof(bitstring) + sizeof(uint_type) - 1) / sizeof(uint_type);
56 static CDS_CONSTEXPR size_t const c_nBitPerByte = 8;
57 static CDS_CONSTEXPR size_t const c_nBitPerHash = sizeof(bitstring) * c_nBitPerByte;
58 static CDS_CONSTEXPR size_t const c_nBitPerInt = sizeof(uint_type) * c_nBitPerByte;
62 /// Initializises the splitter with reference to \p h and zero start bit offset
63 explicit split_bitstring( bitstring const& h )
64 : m_ptr(reinterpret_cast<uint_type const*>( &h ))
68 , m_last( m_ptr + c_nHashSize )
72 /// Initializises the splitter with reference to \p h and start bit offset \p nBitOffset
73 split_bitstring( bitstring const& h, size_t nBitOffset )
74 : m_ptr( reinterpret_cast<uint_type const*>( &h ) + nBitOffset / c_nBitPerInt )
75 , m_offset( nBitOffset )
76 , m_first( reinterpret_cast<uint_type const*>(&h))
78 , m_last( m_first + c_nHashSize )
83 /// Returns \p true if end-of-string is not reached yet
84 explicit operator bool() const
89 /// Returns \p true if end-of-stream encountered
92 return m_offset >= c_nBitPerHash;
95 /// Cuts next \p nBits from bit-string
97 Precondition: <tt>nBits <= sizeof(uint_type) * 8</tt>
99 This function does not manage out-of-bound condition.
100 To control that use \p safe_cut().
102 uint_type cut( size_t nBits )
105 assert( nBits <= c_nBitPerInt );
106 assert( m_offset + nBits <= c_nBitPerHash );
108 assert( m_ptr < m_last );
112 uint_type const nRest = c_nBitPerInt - m_offset % c_nBitPerInt;
114 if ( nBits < nRest ) {
115 result = *m_ptr << ( nRest - nBits );
116 result = result >> ( c_nBitPerInt - nBits );
118 else if ( nBits == nRest ) {
119 result = *m_ptr >> ( c_nBitPerInt - nRest );
121 assert( m_offset % c_nBitPerInt == 0 );
124 uint_type const lsb = *m_ptr >> ( c_nBitPerInt - nRest );
128 result = *m_ptr << ( c_nBitPerInt - nBits );
129 result = result >> ( c_nBitPerInt - nBits );
130 result = (result << nRest) + lsb;
133 assert( m_offset <= c_nBitPerHash );
135 assert( m_ptr <= m_last );
140 /// Cuts up to \p nBits from the bit-string
142 Analog of \p cut() but if \p nBits is more than the rest of bit-string,
143 only the rest is returned.
144 If \p eos() is \p true the function returns 0.
146 uint_type safe_cut( size_t nBits )
151 assert( nBits <= sizeof(uint_type) * c_nBitPerByte );
153 if ( m_offset + nBits > c_nBitPerHash )
154 nBits = c_nBitPerHash - m_offset;
155 return nBits ? cut( nBits ) : 0;
158 /// Resets the splitter
159 void reset() CDS_NOEXCEPT
165 /// Returns pointer to source bitstring
166 bitstring const * source() const
168 return reinterpret_cast<bitstring const *>( m_first );
171 /// Returns current bit offset from beginning of bit-string
172 size_t bit_offset() const
179 uint_type const* m_ptr; ///< current position in the hash
180 size_t m_offset; ///< current bit offset in bit-string
181 uint_type const* m_first; ///< first position
183 uint_type const* m_last; ///< last position
188 }} // namespace cds::algo
190 #endif // #ifndef CDSLIB_ALGO_SPLIT_BITSTRING_H