Compact Variable Length Integer

A variable-width data format for unsigned integers allowing a more compact representation for smaller values. This is sometimes referred to as “compact size” or “var int”.

Format

Numbers are encoded with the first rule that applies of the following:

• If the number < 253 (0xFD), store it in 1 byte, left-padded with zeros.
• If the number fits in 16 bits (but is greater than 252), store it in 3 bytes: a 1-byte value 253 (0xFD) followed by the 2 byte little-endian number.

• If the number fits in 32 bits (but not 8 or 16), store it in 5 bytes: a 1-byte value 254 (0xFE) followed by the 4 byte little-endian number

• If the number fits in 64 bits (but not 8, 16, or 32), store it in 9 bytes: a 1-byte value 255 (0xFF) followed by the 8 byte little-endian number