int.md

Introduction

The Teeworlds protocol has several where 32-bit signed integers are encoded using a variable-length encoding. This documents describes this encoding.

Format

All sizes are specified in bits, from the highest bit in a byte to the lowest.

first_byte:
    [1] flag_extend
    [1] flag_sign
    [6] bits

next_byte:
    [1] flag_extend
    [7] bits

last_byte:
    [4] padding
    [4] bits

int:
    first_byte [next_byte [next_byte [next_byte [last_byte]]]]

As specified, an encoded int can have a size of 1 to 5 bytes. Some bytes have the flag_extend variable which specifies whether they're followed by another byte. The bits of the final integer are the bits fields combined, with a little-endian order. If we call our bits 0 to r, with 0 being the least significant bit, then it looks like this:

ES54 3210  Ecba 9876  Ejih gfed  Eqpo nmlk  PPPP utsr
  ^^ ^^^^   ^^^ ^^^^   ^^^ ^^^^   ^^^ ^^^^       ^^^^

Always use the least amount of bytes possible to encode a number. The padding must always be zeroed.

The flag_sign specifies that all the bits of the resulting number should be flipped, including the sign bit.

NOTE: The reference implementation has no problem with accepting an overlong representation. The reference implementation also interprets the padding as part of the number, which leads to weird results. It should always be zeroed.

Examples

0 is encoded as 0000 0000. 1 is encoded as 0000 0001. -1 is encoded as 0100 0000 (note that the bits field is all zeros).

64 is encoded as 1000 0000 0000 0001.