IxiVarInt Encoding

IxiVarInt is a custom variable-length integer encoding used throughout the Ixian protocol to serialize numeric data in a space-efficient manner. It is not compatible with other common schemes like Protobuf varint or LEB128.

Encoding Principle

The encoding scheme is based on a single-byte prefix which determines the size and type of the integer that follows.

• Unsigned integers from 0 to 247 (0xF7) are encoded as a single byte.
• Larger or negative numbers are encoded using a 1-byte prefix, followed by the integer value in a fixed-size, little-endian format.

Type Prefixes

Prefix	Data Type Represented	Payload Size	Total Bytes	Notes
0x00 - 0xF7	uint8	0 bytes	1	The byte itself is the value.
0xF8	short (negative)	2 bytes	3	Used for IxiVarInt.
0xF9	int (negative)	4 bytes	5	Used for IxiVarInt.
0xFA	long (negative)	8 bytes	9	Used for IxiVarInt.
0xFB	reserved (negative)	? bytes	?	Reserved for potential future use in IxiVarInt.
0xFC	ushort (positive)	2 bytes	3	Used for both IxiVarInt and IxiVarUInt.
0xFD	uint (positive)	4 bytes	5	Used for both IxiVarInt and IxiVarUInt.
0xFE	ulong (positive)	8 bytes	9	Used for both IxiVarInt and IxiVarUInt.
0xFF	reserved (positive)	? bytes	?	Reserved for potential future use in IxiVarUInt.

IxiVarInt vs. IxiVarUInt

The protocol uses two variations depending on whether the integer needs to be signed.

• IxiVarInt (Signed): Can represent both positive and negative integers. It uses the full range of prefixes.
• IxiVarUInt (Unsigned): Can only represent positive integers. Decoders must reject any IxiVarInt that uses the negative-specific prefixes (0xF8, 0xF9, 0xFA).

Examples

• Value: 100
  • As IxiVarUInt: 64 (1 byte, since 100 < 248)
• Value: 1000
  • As IxiVarUInt: FC E8 03 (3 bytes: prefix 0xFC + little-endian ushort for 1000)
• Value: -1000
  • As IxiVarInt: F8 E8 03 (3 bytes: prefix 0xF8 + little-endian ushort for 1000)