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package bitfield
import (
"math/bits"
)
var _ = Bitfield(Bitvector4{})
// Bitvector4 is a bitfield with a known size of 4. There is no length bit
// present in the underlying byte array.
type Bitvector4 []byte
const bitvector4ByteSize = 1
const bitvector4BitSize = 4
// NewBitvector4 creates a new bitvector of size 4.
func NewBitvector4() Bitvector4 {
byteArray := [bitvector4ByteSize]byte{}
return byteArray[:]
}
// BitAt returns the bit value at the given index. If the index requested
// exceeds the number of bits in the bitvector, then this method returns false.
func (b Bitvector4) BitAt(idx uint64) bool {
// Out of bounds, must be false.
if idx >= b.Len() || len(b) != bitvector4ByteSize {
return false
}
i := uint8(1 << idx)
return b[0]&i == i
}
// SetBitAt will set the bit at the given index to the given value. If the index
// requested exceeds the number of bits in the bitvector, then this method returns
// false.
func (b Bitvector4) SetBitAt(idx uint64, val bool) {
// Out of bounds, do nothing.
if idx >= b.Len() || len(b) != bitvector4ByteSize {
return
}
bit := uint8(1 << idx)
if val {
b[0] |= bit
} else {
b[0] &^= bit
}
}
// Len returns the number of bits in the bitvector.
func (b Bitvector4) Len() uint64 {
return bitvector4BitSize
}
// Count returns the number of 1s in the bitvector.
func (b Bitvector4) Count() uint64 {
if len(b) == 0 {
return 0
}
return uint64(bits.OnesCount8(b.Bytes()[0]))
}
// Bytes returns the bytes data representing the bitvector4. This method
// bitmasks the underlying data to ensure that it is an accurate representation.
func (b Bitvector4) Bytes() []byte {
if len(b) == 0 {
return []byte{}
}
return []byte{b[0] & 0x0F}
}
// Shift bitvector by i. If i >= 0, perform left shift, otherwise right shift.
func (b Bitvector4) Shift(i int) {
if len(b) == 0 {
return
}
// Shifting greater than 4 bits is pointless and can have unexpected behavior.
if i > 4 {
i = 4
} else if i < -4 {
i = -4
}
if i >= 0 {
b[0] <<= uint8(i)
} else {
b[0] >>= uint8(i * -1)
}
b[0] &= 0x0F
}
// BitIndices returns the list of indices that are set to 1.
func (b Bitvector4) BitIndices() []int {
indices := make([]int, 0, 4)
for i, bt := range b {
for j := 0; j < 8; j++ {
bit := byte(1 << uint(j))
if bt&bit == bit {
indices = append(indices, i*8+j)
}
}
}
return indices
}
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