Encode and decode TCString

bits.go

@@ -0,0 +1,63 @@
+package iabtcf
+
+type Bits struct {
+	position uint
+	bytes    []byte
+}
+
+var (
+	bytePows = []byte{128, 64, 32, 16, 8, 4, 2, 1}
+)
+
+func NewBits(bytes []byte) *Bits {
+	return &Bits{bytes: bytes, position: 0}
+}
+
+func (b *Bits) ReadBool() bool {
+	byteIndex := b.position / 8
+	bitIndex := b.position % 8
+	b.position++
+
+	return (b.bytes[byteIndex] & bytePows[bitIndex]) != 0
+}
+
+func (b *Bits) WriteBool(v bool) {
+	byteIndex := b.position / 8
+	shift := (byteIndex+1)*8 - b.position - 1
+	b.position++
+
+	if v {
+		b.bytes[byteIndex] |= 1 << uint(shift)
+	} else {
+		b.bytes[byteIndex] &^= 1 << uint(shift)
+	}
+}
+
+func (b *Bits) ReadInt(n uint) int {
+	v := 0
+	for i, shift := uint(0), n-1; i < n; i++ {
+		if b.ReadBool() {
+			v += 1 << uint(shift)
+		}
+		shift--
+	}
+
+	return v
+}
+
+func (b *Bits) WriteInt(v int, n uint) {
+	b.WriteNumber(int64(v), n)
+}
+
+func (b *Bits) WriteNumber(v int64, n uint) {
+	startOffset := int(b.position)
+	for i := int(n) - 1; i >= 0; i-- {
+		index := startOffset + i
+		byteIndex := index / 8
+		shift := (byteIndex+1)*8 - index - 1
+		b.bytes[byteIndex] |= byte(v%2) << uint(shift)
+		v /= 2
+	}
+
+	b.position += n
+}