2 This file is a part of libcds - Concurrent Data Structures library
4 (C) Copyright Maxim Khizhinsky (libcds.dev@gmail.com) 2006-2017
6 Source code repo: http://github.com/khizmax/libcds/
7 Download: http://sourceforge.net/projects/libcds/files/
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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>
48 - \p BitString - a fixed-sized type that interprets as bit string
49 - \p BitStringSize - the size of \p BitString in bytes, default is <tt>sizeof( BitString )</tt>.
50 You can specify 0 for default.
51 - \p UInt - an unsigned integer, return type of \p cut()
53 template <typename BitString, size_t BitStringSize = sizeof( BitString ), typename UInt = typename std::conditional< BitStringSize % sizeof(size_t) == 0, size_t, unsigned >::type >
57 typedef BitString bitstring; ///< Bit-string type
58 typedef UInt uint_type; ///< Bit-string portion type
59 static CDS_CONSTEXPR size_t const c_bitstring_size = BitStringSize ? BitStringSize : sizeof( BitString ); ///< size of \p BitString in bytes
62 static CDS_CONSTEXPR size_t const c_nHashSize = (c_bitstring_size + sizeof(uint_type) - 1) / sizeof(uint_type);
63 static CDS_CONSTEXPR size_t const c_nBitPerByte = 8;
64 static CDS_CONSTEXPR size_t const c_nBitPerHash = c_bitstring_size * c_nBitPerByte;
65 static CDS_CONSTEXPR size_t const c_nBitPerInt = sizeof( uint_type ) * c_nBitPerByte;
69 /// Initializises the splitter with reference to \p h and zero start bit offset
70 explicit split_bitstring( bitstring const& h )
71 : m_ptr(reinterpret_cast<uint_type const*>( &h ))
75 , m_last( m_ptr + c_nHashSize )
79 /// Initializises the splitter with reference to \p h and start bit offset \p nBitOffset
80 split_bitstring( bitstring const& h, size_t nBitOffset )
81 : m_ptr( reinterpret_cast<uint_type const*>( &h ) + nBitOffset / c_nBitPerInt )
82 , m_offset( nBitOffset )
83 , m_first( reinterpret_cast<uint_type const*>(&h))
85 , m_last( m_first + c_nHashSize )
90 /// Returns \p true if end-of-string is not reached yet
91 explicit operator bool() const
96 /// Returns \p true if end-of-stream encountered
99 return m_offset >= c_nBitPerHash;
102 /// Cuts next \p nBits from bit-string
104 Precondition: <tt>nBits <= sizeof(uint_type) * 8</tt>
106 This function does not manage out-of-bound condition.
107 To control that use \p safe_cut().
109 uint_type cut( size_t nBits )
112 assert( nBits <= c_nBitPerInt );
113 assert( m_offset + nBits <= c_nBitPerHash );
115 assert( m_ptr < m_last );
119 uint_type const nRest = c_nBitPerInt - m_offset % c_nBitPerInt;
121 if ( nBits < nRest ) {
122 result = *m_ptr << ( nRest - nBits );
123 result = result >> ( c_nBitPerInt - nBits );
125 else if ( nBits == nRest ) {
126 result = *m_ptr >> ( c_nBitPerInt - nRest );
128 assert( m_offset % c_nBitPerInt == 0 );
131 uint_type const lsb = *m_ptr >> ( c_nBitPerInt - nRest );
135 result = *m_ptr << ( c_nBitPerInt - nBits );
136 result = result >> ( c_nBitPerInt - nBits );
137 result = (result << nRest) + lsb;
140 assert( m_offset <= c_nBitPerHash );
142 assert( m_ptr <= m_last );
147 /// Cuts up to \p nBits from the bit-string
149 Analog of \p cut() but if \p nBits is more than the rest of bit-string,
150 only the rest is returned.
151 If \p eos() is \p true the function returns 0.
153 uint_type safe_cut( size_t nBits )
158 assert( nBits <= sizeof(uint_type) * c_nBitPerByte );
160 if ( m_offset + nBits > c_nBitPerHash )
161 nBits = c_nBitPerHash - m_offset;
162 return nBits ? cut( nBits ) : 0;
165 /// Resets the splitter
166 void reset() CDS_NOEXCEPT
172 /// Returns pointer to source bitstring
173 bitstring const * source() const
175 return reinterpret_cast<bitstring const *>( m_first );
178 /// Returns current bit offset from beginning of bit-string
179 size_t bit_offset() const
186 uint_type const* m_ptr; ///< current position in the hash
187 size_t m_offset; ///< current bit offset in bit-string
188 uint_type const* m_first; ///< first position
190 uint_type const* m_last; ///< last position
195 }} // namespace cds::algo
197 #endif // #ifndef CDSLIB_ALGO_SPLIT_BITSTRING_H