Data types

Revision as of 03:14, 25 March 2015 by Fenhl (talk | contribs) (→‎Position: handling negative coordinates)
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All data sent over the network is big-endian, that is the bytes are sent from most significant byte to least significant byte. The majority of everyday computers are little-endian, therefore it may be necessary to change the endianness before sending data over the network.

Name Size (bytes) Encodes Notes
Boolean 1 false or true Value can be either true (0x01) or false (0x00)
Byte 1 -128 to 127 Signed 8-bit integer, two's complement
Unsigned Byte 1 0 to 255 Unsigned 8-bit integer
Short 2 -32768 to 32767 Signed 16-bit integer, two's complement
Unsigned Short 2 0 to 65535 Unsigned 16-bit integer
Int 4 -2147483648 to 2147483647 Signed 32-bit integer, two's complement
Long 8 -9223372036854775808 to 9223372036854775807 Signed 64-bit integer, two's complement
Float 4 Single-precision 32-bit IEEE 754 floating point
Double 8 Double-precision 64-bit IEEE 754 floating point
String ≥ 1
≤ 2147483652
A sequence of Unicode code points UTF-8 string prefixed with its size in bytes as a VarInt
Chat ≥ 1
≤ 2147483652
See Chat Encoded as a String
VarInt ≥ 1
≤ 5
-2147483648 to 2147483647 Protocol Buffer Varint, encoding a two's complement signed 32-bit integer
VarLong ≥ 1
≤ 10
-9223372036854775808 to 9223372036854775807 Protocol Buffer Varint, encoding a two's complement signed 64-bit integer
Chunk Varies A vertical chunk column See SMP Map Format#Data
Metadata Varies See Entities#Entity Metadata Format
Slot Varies See Slot Data
Object Data 4 or 10 See Object Data
NBT Tag Varies See NBT
Position 8 Integer/block position: x (-33554432 to 33554431), y (-2048 to 2047), z (-33554432 to 33554431) x as a 26-bit integer, followed by y as a 12-bit integer, followed by z as a 26-bit integer (all signed, two's complement). See also the section below.
Angle 1 Rotation angle in steps of 1/256 of a full turn Whether or not this is signed does not matter, since the resulting angles are the same.
UUID 16 A UUID The vanilla Minecraft server internally sends this as two longs.
Optional X 0 or size of X A field of type X, or nothing Whether or not the field is present must be known from the context.
Array of X count times size of X Zero or more fields of type X The count must be known from the context.
Byte Array Varies Depends on context This is just a sequence of zero or more bytes, its meaning should be explained somewhere else, e.g. in the packet description. The length must also be known from the context.


64-bit value split in to three parts

  • x: 26 MSBs
  • z: 26 LSBs
  • y: 12 bits between them

Encoded as followed:

((x & 0x3FFFFFF) << 38) | ((y & 0xFFF) << 26) | (z & 0x3FFFFFF)

And decoded as:

long val; // Encoded value
x = val >> 38;
y = (val >> 26) & 0xFFF
z = val << 38 >> 38

Note: The details of bit shifting are rather language dependent; the above may work in Java but probably won't in other languages without some tweaking. In particular, you will usually receive positive numbers even if the actual coordinates are negative. This can be fixed by adding something like the following:

if x >= 2^25 { x -= 2^26 }
if y >= 2^11 { y -= 2^12 }
if z >= 2^25 { z -= 2^26 }

Fixed-point numbers

Some fields may be stored as fixed-point numbers, where a certain number of bits represents the signed integer part (number to the left of the decimal point) and the rest represents the fractional part (to the right). Floating points (float and double), in contrast, keep the number itself (mantissa) in one chunk, while the location of the decimal point (exponent) is stored beside it.

Essentially, while fixed-point numbers have lower range than floating points, their fractional precision is greater for higher values. This makes them ideal for representing global coordinates of an entity in Minecraft, as it's more important to store the integer part accurately than position them more precisely within a single block (or meter).

Coordinates are often represented as a 32-bit integer, where 5 of the least-significant bits are dedicated to the fractional part, and the rest store the integer part.

Java lacks support for fractional integers directly, but you can represent them as integers. To convert from a double to this integer representation, use the following formulas:

 abs_int = (int)double * 32;

And back again:

 double = (double)abs_int / 32;