README
¶
Variable Length Quantity
A go implementation of the VLQ type. VLQ is an encoding scheme to compress unsigned integers.
Library Usage
func readme_example_normal() {
// Standard operation
value := Rvlq(30000)
byteCount := value.EncodedSize()
buffer := make([]byte, byteCount)
value.EncodeTo(buffer)
fmt.Printf("Encoded %v into the byte sequence %v\n", value, buffer)
decodedValue, bytesUsed, isComplete := DecodeRvlqFrom(buffer)
if !isComplete {
// TODO: Error handling
}
fmt.Printf("Decoded value %v from %v bytes\n", decodedValue, bytesUsed)
}
Result:
Encoded 30000 into the byte sequence [129 234 48]
Decoded value 30000 from 3 bytes
func readme_example_split_reads() {
// Simulate the VLQ being split across two reads
value := Rvlq(30000)
byteCount := value.EncodedSize()
buffer := make([]byte, byteCount)
value.EncodeTo(buffer)
buffer1 := buffer[:2]
buffer2 := buffer[2:]
var decodedValue Rvlq
bytesUsed, isComplete := decodedValue.DecodeFrom(buffer1)
fmt.Printf("Used %v bytes decoding VLQ value. Is complete = %v\n", bytesUsed, isComplete)
bytesUsed, isComplete = decodedValue.DecodeFrom(buffer2)
fmt.Printf("Used %v bytes decoding VLQ value. Is complete = %v\n", bytesUsed, isComplete)
fmt.Printf("Decoded value: %v\n", decodedValue)
}
Result:
Used 2 bytes decoding VLQ value. Is complete = false
Used 1 bytes decoding VLQ value. Is complete = true
Decoded value: 30000
func readme_example_reversed() {
// Reversed mode, which allows reading the value from the end of a buffer
value := Rvlq(30000)
buffer := make([]byte, 10)
value.EncodeReversedTo(buffer)
fmt.Printf("Encoded %v into the byte sequence %v\n", value, buffer)
decodedValue, bytesUsed, ok := DecodeRvlqReversedFrom(buffer)
if !ok {
// TODO: Didn't find end of sequence
}
fmt.Printf("Decoded value %v from %v bytes\n", decodedValue, bytesUsed)
}
Result:
Encoded 30000 into the byte sequence [0 0 0 0 0 0 0 48 234 129]
Decoded value 30000 from 3 bytes
Documentation
¶
Overview ¶
VLQ (Variable Length Quantity) is an unsigned integer encoding scheme designed for the MIDI file format.
It encodes a value into a sequence of bytes where the lower 7 bits contain data and the high bit is used as a "continuation" bit. A decoder reads encoded bytes, filling a decoded unsigned integer 7 bits at a time in big endian order, until it encounters a byte with the high "continuation" bit cleared.
Index ¶
- Constants
- func Extend(buffer []byte, groupCount int) (bytesEncoded int, err error)
- func IsExtended(buffer []byte) bool
- func MaxValueInBytes(byteCount int) uint64
- type Lvlq
- func (this *Lvlq) DecodeFrom(buffer []byte) (decodedByteCount int, isComplete bool)
- func (this *Lvlq) DecodeReversedFrom(buffer []byte) (decodedByteCount int, ok bool)
- func (this Lvlq) EncodeReversedTo(buffer []byte) (encodedByteCount int, ok bool)
- func (this Lvlq) EncodeTo(buffer []byte) (encodedByteCount int, ok bool)
- func (this Lvlq) EncodedSize() int
- type Rvlq
- func (this *Rvlq) DecodeFrom(buffer []byte) (decodedByteCount int, isComplete bool)
- func (this *Rvlq) DecodeReversedFrom(buffer []byte) (decodedByteCount int, ok bool)
- func (this Rvlq) EncodeReversedTo(buffer []byte) (encodedByteCount int, ok bool)
- func (this Rvlq) EncodeTo(buffer []byte) (encodedByteCount int, ok bool)
- func (this Rvlq) EncodedSize() int
Constants ¶
const MaxEncodeLength = 10
Maximum byte length that this library will encode (for a 64-bit value)
Variables ¶
This section is empty.
Functions ¶
func IsExtended ¶
Returns true if the encoded VLQ is extended (prepended with 0x80)
func MaxValueInBytes ¶
Get the maximum value that can be stored in a RVLQ of the selected byte count
Types ¶
type Lvlq ¶
type Lvlq uint64
func DecodeLvlqFrom ¶
func DecodeLvlqReversedFrom ¶
Decode a RVLQ value in reverse order from the end of a buffer. Unlike DecodeFrom(), the reversed version must have all encoded bytes present in the buffer to decode.
func (*Lvlq) DecodeFrom ¶
Decode this LVLQ from a buffer. Returns true for isComplete once the VLQ is fully decoded (i.e. it has encountered a byte with the high bit cleared). This allows for progressive decoding of the VLQ value across multiple buffers.
func (*Lvlq) DecodeReversedFrom ¶
Decode this RVLQ in reverse order from the end of a buffer. Unlike DecodeFrom(), the reversed version must have all encoded bytes present in the buffer to decode.
func (Lvlq) EncodeReversedTo ¶
Encode this LVLQ in reverse order to the end of a buffer. Returns false and the number of bytes it attempted to write if the buffer isn't big enough.
func (Lvlq) EncodeTo ¶
Encode this LVLQ to a buffer. Returns false and the number of bytes it attempted to write if the buffer isn't big enough.
func (Lvlq) EncodedSize ¶
Get the number of bytes required to encode this RVLQ
type Rvlq ¶
type Rvlq uint64
func DecodeRvlqFrom ¶
func DecodeRvlqReversedFrom ¶
Decode a RVLQ value in reverse order from the end of a buffer. Unlike DecodeFrom(), the reversed version must have all encoded bytes present in the buffer to decode.
func (*Rvlq) DecodeFrom ¶
Decode this RVLQ from a buffer. Returns true for isComplete once the VLQ is fully decoded (i.e. it has encountered a byte with the high bit cleared). This allows for progressive decoding of the VLQ value across multiple buffers.
func (*Rvlq) DecodeReversedFrom ¶
Decode this RVLQ in reverse order from the end of a buffer. Unlike DecodeFrom(), the reversed version must have all encoded bytes present in the buffer to decode.
func (Rvlq) EncodeReversedTo ¶
Encode this RVLQ in reverse order to the end of a buffer. Returns false and the number of bytes it attempted to write if the buffer isn't big enough.
func (Rvlq) EncodeTo ¶
Encode this RVLQ to a buffer. Returns false and the number of bytes it attempted to write if the buffer isn't big enough.
func (Rvlq) EncodedSize ¶
Get the number of bytes required to encode this RVLQ
Source Files