boolmap - nibblemap.go

     1  package boolmap
     2  
     3  // NibbleMap is a map of Nibbles (4-bits, values 0-15)
     4  type NibbleMap map[uint64]byte
     5  
     6  // NewNibbleMap return a new, initialised, NibbleMap
     7  func NewNibbleMap() NibbleMap {
     8  	return make(NibbleMap)
     9  }
    10  
    11  // Get returns a crumb from the given position
    12  func (n NibbleMap) Get(p uint64) byte {
    13  	d := n[p>>1]
    14  	if p&1 == 0 {
    15  		return d & 15
    16  	}
    17  	return d >> 4
    18  }
    19  
    20  // Set sets the crumb at the given position
    21  func (n NibbleMap) Set(p uint64, d byte) {
    22  	pos := p >> 1
    23  	oldData, ok := n[pos]
    24  	if !ok && d == 0 {
    25  		return
    26  	}
    27  	if p&1 == 0 {
    28  		d = oldData&240 | d&15
    29  	} else {
    30  		d = oldData&15 | d<<4
    31  	}
    32  	if d == 0 {
    33  		delete(n, pos)
    34  	} else {
    35  		n[pos] = d
    36  	}
    37  }
    38  
    39  // NibbleSlice is a slice of bytes representing nibbles (4-bits)
    40  type NibbleSlice []byte
    41  
    42  // NewNibbleSlice returns a new, initialised, CrumbSlice
    43  func NewNibbleSlice() NibbleSlice {
    44  	return NewNibbleSliceSize(1)
    45  }
    46  
    47  // NewNibbleSliceSize returns a new NibbleSlice, initialised to the given size
    48  func NewNibbleSliceSize(size uint) NibbleSlice {
    49  	sliceSize := size >> 1
    50  	if size&1 != 0 {
    51  		sliceSize++
    52  	}
    53  	return make(NibbleSlice, sliceSize)
    54  }
    55  
    56  // Get returns a crumb from the given position
    57  func (n NibbleSlice) Get(p uint) byte {
    58  	pos := p >> 1
    59  	if pos >= uint(len(n)) {
    60  		return 0
    61  	}
    62  	d := n[pos]
    63  	if p&1 == 0 {
    64  		return d & 15
    65  	}
    66  	return d >> 4
    67  }
    68  
    69  // Set sets the crumb at the given position
    70  func (n *NibbleSlice) Set(p uint, d byte) {
    71  	pos := p >> 1
    72  	if pos >= uint(len(*n)) {
    73  		if d == 0 {
    74  			return
    75  		}
    76  		if pos < uint(cap(*n)) {
    77  			*n = (*n)[:cap(*n)]
    78  		} else {
    79  			var newData NibbleSlice
    80  			if pos < 512 {
    81  				newData = make([]byte, pos<<1)
    82  			} else {
    83  				newData = make([]byte, pos+(pos>>2))
    84  			}
    85  			copy(newData, *n)
    86  			*n = newData
    87  		}
    88  	}
    89  	oldData := (*n)[pos]
    90  	if p&1 == 0 {
    91  		d = oldData&240 | d&15
    92  	} else {
    93  		d = oldData&15 | d<<4
    94  	}
    95  	(*n)[pos] = d
    96  }