VLQencoded

VLQencoded refers to the use of Variable Length Quantity (VLQ) encoding to represent integers with a variable number of bytes. In a VLQ stream, each byte contains seven data bits and a continuation flag in the most significant bit. The continuation flag is set to 1 when another byte follows and cleared to 0 for the final byte. The seven data bits from each byte contribute to the overall value, with the most significant group appearing first.

To encode a value, the number is split into 7-bit chunks. These chunks are arranged in big-endian order (most significant first). All bytes except the last have their MSB set to 1, while the last byte has the MSB set to 0. This yields a compact representation for small numbers while allowing larger values to be represented without a fixed upper bound on length.

Decoding VLQencoded data involves reading bytes until a byte with MSB 0 is encountered, collecting the seven data bits from each byte in order and reconstructing the original integer. The method is efficient for data with many small values, as it uses fewer bytes on average.

Applications of VLQencoded data include the MIDI file format, where delta times and other quantities are stored as VLQs, as well as various serialization schemes and protocols that favor compact, self-delimiting integers. VLQ encoding is related to other variable-length integer schemes such as LEB128 and Google varint, though differences in endianness and continuation rules distinguish their implementations.

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