# Difference between revisions of "Data types"

m (→Fixed-point numbers: typo) |
m (→Position: decode and encode fix) |
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Encoded as followed: | Encoded as followed: | ||

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

Line 103: | Line 103: | ||

long val; // Encoded value | long val; // Encoded value | ||

x = val >> 38; | x = val >> 38; | ||

− | y = val | + | y = (val >> 26) & 0xFFF |

− | z = val << 38 >> 38 | + | z = (val << 38) >> 38 |

=== Fixed-point numbers === | === Fixed-point numbers === |

## Revision as of 10:28, 27 September 2014

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.

Other than 'String' and 'Metadata', which are decoded with a custom function, these data formats are identical to those provided by the Java classes DataInputStream and DataOutputStream.

Size | Range | Notes | |
---|---|---|---|

bool | 1 | 0 or 1 | Value can be either true (0x01) or false (0x00) |

byte | 1 | -128 to 127 | Signed, two's complement |

short | 2 | -32768 to 32767 | Signed, two's complement |

int | 4 | -2147483648 to 2147483647 | Signed, two's complement |

long | 8 | -9223372036854775808 to 9223372036854775807 | Signed, two's complement |

128-bit integer | 16 | 0 to 340282366920938463463374607431768211455 | Unsigned, two's complement
Used in 0x2C to transmit UUIDs. The vanilla Minecraft server internally sends this as two longs. |

float | 4 |
See this |
Single-precision 32-bit IEEE 754 floating point |

double | 8 |
See this |
Double-precision 64-bit IEEE 754 floating point |

string | ≥ 2 ≤ 240 |
N/A | UTF-8 String length prefixed with a VarInt |

VarInt | Varies | Protocol Buffer 32-bit Varint | |

VarLong | Varies | Like VarInt but for java longs | |

metadata | Varies | See this | |

Slot Data | Varies | See slot data | |

Position | 8 | See below | |

UUID | 16 | Encoded as two longs this.writeLong(uuid.getMostSignificantBits()); this.writeLong(uuid.getLeastSignificantBits()); |

### Position

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

### 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;