boolmap - boolmap.go

     1  // Package boolmap creates a map of bools using bytes for efficiency (needs benchmarking for memory)
     2  package boolmap // import "vimagination.zapto.org/boolmap"
     3  
     4  // Map is the default boolmap
     5  type Map map[uint64]byte
     6  
     7  // NewMap returns a new, initialised Map
     8  func NewMap() Map {
     9  	return make(Map)
    10  }
    11  
    12  // Get returns a bool, represented by a byte, for the specified position
    13  func (m Map) Get(p uint64) byte {
    14  	if m.GetBool(p) {
    15  		return 1
    16  	}
    17  	return 0
    18  }
    19  
    20  // GetBool returns a bool for the specified position
    21  func (m Map) GetBool(p uint64) bool {
    22  	return m[p>>3]&(1<<(p&7)) != 0
    23  }
    24  
    25  // Set sets a bool, represented by a byte, at the specified position
    26  func (m Map) Set(p uint64, d byte) {
    27  	m.SetBool(p, d != 0)
    28  }
    29  
    30  // SetBool sets a bool at the specified position
    31  func (m Map) SetBool(p uint64, d bool) {
    32  	shift := byte(1 << (p & 7))
    33  	pos := p >> 3
    34  	c, ok := m[pos]
    35  	if !ok && !d {
    36  		return
    37  	}
    38  	if d {
    39  		c |= shift
    40  	} else {
    41  		c &^= shift
    42  	}
    43  	if c == 0 {
    44  		delete(m, pos)
    45  	} else {
    46  		m[pos] = c
    47  	}
    48  }
    49  
    50  // Slice is a slice of bytes representing bools
    51  type Slice []byte
    52  
    53  // NewSlice returnns a new, initialised Slice
    54  func NewSlice() *Slice {
    55  	return NewSliceSize(1)
    56  }
    57  
    58  // NewSliceSize returns a new Slice, intitialised to the size given
    59  func NewSliceSize(size uint) *Slice {
    60  	sliceSize := size >> 3
    61  	if size&7 != 0 {
    62  		sliceSize++
    63  	}
    64  	s := make(Slice, sliceSize)
    65  	return &s
    66  }
    67  
    68  // Get returns a byte, representing a bool, at the specified position
    69  func (s Slice) Get(p uint) byte {
    70  	if s.GetBool(p) {
    71  		return 1
    72  	}
    73  	return 0
    74  }
    75  
    76  // GetBool returns a bool for the specified position
    77  func (s Slice) GetBool(p uint) bool {
    78  	pos := p >> 3
    79  	if pos > uint(len(s)) {
    80  		return false
    81  	}
    82  	return s[pos]&(1<<(p&7)) != 0
    83  }
    84  
    85  // Set sets a bool, given as a byte, at the specified position
    86  func (s *Slice) Set(p uint, d byte) {
    87  	s.SetBool(p, d != 0)
    88  }
    89  
    90  // SetBool sets a bool at the specified position
    91  func (s *Slice) SetBool(p uint, d bool) {
    92  	pos := p >> 3
    93  	if pos >= uint(len(*s)) {
    94  		if !d {
    95  			return
    96  		}
    97  		if pos < uint(cap(*s)) {
    98  			*s = (*s)[:cap(*s)]
    99  		} else {
   100  			var newData Slice
   101  			if pos < 512 {
   102  				newData = make(Slice, pos<<1)
   103  			} else {
   104  				newData = make(Slice, pos+(pos>>2))
   105  			}
   106  			copy(newData, *s)
   107  			*s = newData
   108  		}
   109  	}
   110  	shift := byte(1 << (p & 7))
   111  	if d {
   112  		(*s)[pos] |= shift
   113  	} else {
   114  		(*s)[pos] &^= shift
   115  	}
   116  }