@ -15,37 +15,172 @@
namespace ROCKSDB_NAMESPACE {
// This is a data structure specifically designed as a "Set" for a
// pretty small scale of Enum structure. For now, it can support up
// to 64 element, and it is expandable in the future.
template < typename ENUM_TYPE , ENUM_TYPE MAX_VALUE >
namespace detail {
int CountTrailingZeroBitsForSmallEnumSet ( uint64_t ) ;
} // namespace detail
// Represents a set of values of some enum type with a small number of
// possible enumerators. For now, it supports enums where no enumerator
// exceeds 63 when converted to int.
template < typename ENUM_TYPE , ENUM_TYPE MAX_ENUMERATOR >
class SmallEnumSet {
private :
using StateT = uint64_t ;
static constexpr int kStateBits = sizeof ( StateT ) * 8 ;
static constexpr int kMaxMax = kStateBits - 1 ;
static constexpr int kMaxValue = static_cast < int > ( MAX_ENUMERATOR ) ;
static_assert ( kMaxValue > = 0 ) ;
static_assert ( kMaxValue < = kMaxMax ) ;
public :
// construct / create
SmallEnumSet ( ) : state_ ( 0 ) { }
~ SmallEnumSet ( ) { }
template < class . . . TRest >
/*implicit*/ constexpr SmallEnumSet ( const ENUM_TYPE e , TRest . . . rest ) {
* this = SmallEnumSet ( rest . . . ) . With ( e ) ;
}
// Return true if the input enum is included in the "Set" (i.e., changes the
// internal scalar state successfully), otherwise, it will return false.
bool Add ( const ENUM_TYPE value ) {
static_assert ( MAX_VALUE < = 63 , " Size currently limited to 64 " ) ;
assert ( value > = 0 & & value < = MAX_VALUE ) ;
uint64_t old_state = state_ ;
uint64_t tmp = 1 ;
state_ | = ( tmp < < value ) ;
return old_state ! = state_ ;
// Return the set that includes all valid values, assuming the enum
// is "dense" (includes all values converting to 0 through kMaxValue)
static constexpr SmallEnumSet All ( ) {
StateT tmp = StateT { 1 } < < kMaxValue ;
return SmallEnumSet ( RawStateMarker ( ) , tmp | ( tmp - 1 ) ) ;
}
// equality
bool operator = = ( const SmallEnumSet & that ) const {
return this - > state_ = = that . state_ ;
}
bool operator ! = ( const SmallEnumSet & that ) const { return ! ( * this = = that ) ; }
// query
// Return true if the input enum is contained in the "Set".
bool Contains ( const ENUM_TYPE value ) {
static_assert ( MAX_VALUE < = 63 , " Size currently limited to 64 " ) ;
assert ( value > = 0 & & value < = MAX_VALUE ) ;
uint64_t tmp = 1 ;
bool Contains ( const ENUM_TYPE e ) const {
int value = static_cast < int > ( e ) ;
assert ( value > = 0 & & value < = kMaxValue ) ;
StateT tmp = 1 ;
return state_ & ( tmp < < value ) ;
}
bool empty ( ) const { return state_ = = 0 ; }
// iterator
class const_iterator {
public :
// copy
const_iterator ( const const_iterator & that ) = default ;
const_iterator & operator = ( const const_iterator & that ) = default ;
// move
const_iterator ( const_iterator & & that ) noexcept = default ;
const_iterator & operator = ( const_iterator & & that ) noexcept = default ;
// equality
bool operator = = ( const const_iterator & that ) const {
assert ( set_ = = that . set_ ) ;
return this - > pos_ = = that . pos_ ;
}
bool operator ! = ( const const_iterator & that ) const {
return ! ( * this = = that ) ;
}
// ++iterator
const_iterator & operator + + ( ) {
if ( pos_ < kMaxValue ) {
pos_ = set_ - > SkipUnset ( pos_ + 1 ) ;
} else {
pos_ = kStateBits ;
}
return * this ;
}
// iterator++
const_iterator operator + + ( int ) {
auto old = * this ;
+ + * this ;
return old ;
}
ENUM_TYPE operator * ( ) const {
assert ( pos_ < = kMaxValue ) ;
return static_cast < ENUM_TYPE > ( pos_ ) ;
}
private :
friend class SmallEnumSet ;
const_iterator ( const SmallEnumSet * set , int pos ) : set_ ( set ) , pos_ ( pos ) { }
const SmallEnumSet * set_ ;
int pos_ ;
} ;
const_iterator begin ( ) const { return const_iterator ( this , SkipUnset ( 0 ) ) ; }
const_iterator end ( ) const { return const_iterator ( this , kStateBits ) ; }
// mutable ops
// Modifies the set (if needed) to include the given value. Returns true
// iff the set was modified.
bool Add ( const ENUM_TYPE e ) {
int value = static_cast < int > ( e ) ;
assert ( value > = 0 & & value < = kMaxValue ) ;
StateT old_state = state_ ;
state_ | = ( StateT { 1 } < < value ) ;
return old_state ! = state_ ;
}
// Modifies the set (if needed) not to include the given value. Returns true
// iff the set was modified.
bool Remove ( const ENUM_TYPE e ) {
int value = static_cast < int > ( e ) ;
assert ( value > = 0 & & value < = kMaxValue ) ;
StateT old_state = state_ ;
state_ & = ~ ( StateT { 1 } < < value ) ;
return old_state ! = state_ ;
}
// applicative ops
// Return a new set based on this one with the additional value(s) inserted
constexpr SmallEnumSet With ( const ENUM_TYPE e ) const {
int value = static_cast < int > ( e ) ;
assert ( value > = 0 & & value < = kMaxValue ) ;
return SmallEnumSet ( RawStateMarker ( ) , state_ | ( StateT { 1 } < < value ) ) ;
}
template < class . . . TRest >
constexpr SmallEnumSet With ( const ENUM_TYPE e1 , const ENUM_TYPE e2 ,
TRest . . . rest ) const {
return With ( e1 ) . With ( e2 , rest . . . ) ;
}
// Return a new set based on this one excluding the given value(s)
constexpr SmallEnumSet Without ( const ENUM_TYPE e ) const {
int value = static_cast < int > ( e ) ;
assert ( value > = 0 & & value < = kMaxValue ) ;
return SmallEnumSet ( RawStateMarker ( ) , state_ & ~ ( StateT { 1 } < < value ) ) ;
}
template < class . . . TRest >
constexpr SmallEnumSet Without ( const ENUM_TYPE e1 , const ENUM_TYPE e2 ,
TRest . . . rest ) const {
return Without ( e1 ) . Without ( e2 , rest . . . ) ;
}
private :
uint64_t state_ ;
int SkipUnset ( int pos ) const {
StateT tmp = state_ > > pos ;
if ( tmp = = 0 ) {
return kStateBits ;
} else {
return pos + detail : : CountTrailingZeroBitsForSmallEnumSet ( tmp ) ;
}
}
struct RawStateMarker { } ;
explicit SmallEnumSet ( RawStateMarker , StateT state ) : state_ ( state ) { }
StateT state_ ;
} ;
} // namespace ROCKSDB_NAMESPACE
Peter Dillinger
2 years ago
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