3 #ifndef CDSLIB_ALGO_SPLIT_BITSTRING_H
4 #define CDSLIB_ALGO_SPLIT_BITSTRING_H
6 #include <cds/algo/base.h>
8 namespace cds { namespace algo {
10 /// Cuts a bit sequence from fixed-size bit-string
12 The splitter an be used as iterator over bit-string.
13 Each call of \p cut() or \p safe_cut() cuts the bit count specified
14 and keeps the position inside bit-string for the next call.
16 The splitter stores a const reference to bit-string, not a copy.
17 The maximum count of bits that can be cut for single call is <tt> sizeof(UInt) * 8 </tt>
19 template <typename BitString, typename UInt = size_t >
23 typedef BitString bitstring; ///< Bit-string type
24 typedef UInt uint_type; ///< Bit-string portion type
27 static CDS_CONSTEXPR size_t const c_nHashSize = (sizeof(bitstring) + sizeof(uint_type) - 1) / sizeof(uint_type);
28 static CDS_CONSTEXPR size_t const c_nBitPerByte = 8;
29 static CDS_CONSTEXPR size_t const c_nBitPerHash = sizeof(bitstring) * c_nBitPerByte;
30 static CDS_CONSTEXPR size_t const c_nBitPerInt = sizeof(uint_type) * c_nBitPerByte;
34 /// Initializises the splitter with reference to \p h
35 explicit split_bitstring( bitstring const& h )
36 : m_ptr(reinterpret_cast<uint_type const*>( &h ))
40 , m_last( m_ptr + c_nHashSize )
44 /// Returns \p true if end-of-string is not reached yet
45 explicit operator bool() const
50 /// Returns \p true if end-of-stream encountered
53 return m_pos >= c_nBitPerHash;
56 /// Cuts next \p nBits from bit-string
58 Precondition: <tt>nBits <= sizeof(uint_type) * 8</tt>
60 This function does not manage out-of-bound condition.
61 To control that use \p safe_cut().
63 uint_type cut( size_t nBits )
66 assert( nBits <= c_nBitPerInt );
67 assert( m_pos + nBits <= c_nBitPerHash );
69 assert( m_ptr < m_last );
73 uint_type const nRest = c_nBitPerInt - m_pos % c_nBitPerInt;
75 if ( nBits < nRest ) {
76 result = *m_ptr << ( nRest - nBits );
77 result = result >> ( c_nBitPerInt - nBits );
79 else if ( nBits == nRest ) {
80 result = *m_ptr >> ( c_nBitPerInt - nRest );
84 uint_type const lsb = *m_ptr >> ( c_nBitPerInt - nRest );
88 result = *m_ptr << ( c_nBitPerInt - nBits );
89 result = result >> ( c_nBitPerInt - nBits );
90 result = (result << nRest) + lsb;
93 assert( m_pos <= c_nBitPerHash );
95 assert( m_ptr <= m_last );
100 /// Cuts up to \p nBits from the bit-string
102 Analog of \p cut() but if \p nBits is more than the rest of bit-string,
103 only the rest is returned.
104 If \p eos() is \p true the function returns 0.
106 uint_type safe_cut( size_t nBits )
111 assert( nBits <= sizeof(uint_type) * c_nBitPerByte );
113 if ( m_pos + nBits > c_nBitPerHash )
114 nBits = c_nBitPerHash - m_pos;
115 return nBits ? cut( nBits ) : 0;
118 /// Resets the splitter
127 uint_type const* m_ptr; ///< current position in the hash
128 size_t m_pos; ///< current position in bits
129 uint_type const* m_first; ///< first position
131 uint_type const* m_last; ///< last position
136 }} // namespace cds::algo
138 #endif // #ifndef CDSLIB_ALGO_SPLIT_BITSTRING_H