Function DecodeValueTag

pkg/util/encoding/encoding.go:2036–2062

DecodeValueTag decodes a value encoded by EncodeValueTag, used as a prefix in each of the other EncodeFooValue methods. The tag is structured such that the encoded column id can be dropped from the front by removing the first `typeOffset` bytes. DecodeValueTag, PeekValueLength and each of the Decod

(b []byte)

// will return the same thing. PeekValueLength works as expected with either of
// `b` or `b[typeOffset:]`.
func DecodeValueTag(b []byte) (typeOffset int, dataOffset int, colID uint32, typ Type, err error) {
	// TODO(dan): This can be made faster by special casing the single byte
	// version and skipping the column id extraction when it's not needed.
	if len(b) == 0 {
		return 0, 0, 0, Unknown, fmt.Errorf("empty array")
	}
	var n int
	var tag uint64
	b, n, tag, err = DecodeNonsortingUvarint(b)
	if err != nil {
		return 0, 0, 0, Unknown, err
	}
	colID = uint32(tag >> 4)

	typ = Type(tag & 0xf)
	typeOffset = n - 1
	dataOffset = n
	if typ == SentinelType {
		_, n, tag, err = DecodeNonsortingUvarint(b)
		if err != nil {
			return 0, 0, 0, Unknown, err
		}
		typ = Type(tag)
		dataOffset += n
	}
	return typeOffset, dataOffset, colID, typ, nil
}

// DecodeBoolValue decodes a value encoded by EncodeBoolValue.
func DecodeBoolValue(buf []byte) (remaining []byte, b bool, err error) {