bitmask - bitmask.go

     1  // Package bitmask implements a simple bitmask type
     2  package bitmask // import "vimagination.zapto.org/bitmask"
     3  
     4  // BitMask is the main type. It is completely safe to cast from an existing byte
     5  // slice or to create a BitMask with make.
     6  type BitMask []byte
     7  
     8  // New creates a new BitMask with enough storage to hold at least the required
     9  // number of bits.
    10  func New(bits int) BitMask {
    11  	numCells := bits >> 3
    12  	if bits&7 != 0 {
    13  		numCells++
    14  	}
    15  	return make(BitMask, numCells)
    16  }
    17  
    18  // Get will retrieve the bool stored at given bit position.
    19  func (b BitMask) Get(bit int) bool {
    20  	pos := bit >> 3
    21  	if pos > len(b) {
    22  		return false
    23  	}
    24  	return b[pos]&byte(1<<byte(bit&7)) != 0
    25  }
    26  
    27  // Set will set the given bool at the given position.
    28  func (b BitMask) Set(bit int, d bool) {
    29  	pos := bit >> 3
    30  	if pos > len(b) {
    31  		return
    32  	}
    33  	shift := byte(1 << byte(bit&7))
    34  	if d {
    35  		b[pos] |= shift
    36  	} else {
    37  		b[pos] &^= shift
    38  	}
    39  }
    40  
    41  // SetIfNot will set the given bool at the given position and return true if
    42  // the value has changed.
    43  func (b BitMask) SetIfNot(bit int, d bool) bool {
    44  	pos := bit >> 3
    45  	if pos > len(b) {
    46  		return false
    47  	}
    48  	if (b[pos]&byte(1<<byte(bit&7)) != 0) == d {
    49  		return false
    50  	}
    51  	shift := byte(1 << byte(bit&7))
    52  	if d {
    53  		b[pos] |= shift
    54  	} else {
    55  		b[pos] &^= shift
    56  	}
    57  	return true
    58  }