### 4 releases (2 breaking)

0.2.0 | May 17, 2020 |
---|---|

0.1.1 | Feb 19, 2020 |

0.1.0 | Feb 19, 2020 |

0.0.0 | Jul 10, 2018 |

**2,229** downloads per month

Used in **5** crates
(via ggrs)

**MIT/Apache**

15KB

172 lines

# bitfield-rle

A run-length-encoder that compresses bitfields.

The encoder uses a compact format and will only run length encode sequences of bits if it compresses the bitfield. The encoded bitfield should therefore always be smaller or the same size as the original bitfield with the exception of a 1-6 byte header.

Since this uses run-length-encoding, you'll get the best compression results if you have longer sequences of the same bit in your bitfield.

## Usage

`extern` `crate` bitfield_rle`;`
`extern` `crate` sparse_bitfield`;`
`use` `sparse_bitfield``::`Bitfield`;`
`let` `mut` bits `=` `Bitfield``::`new`(``1024``)``;`
bits`.``set``(``400``,` `true``)``;`
`let` enc `=` `bitfield_rle``::`encode`(`bits`)``;`
`assert_eq!``(`enc`.``len``(``)``,` `6``)``;`
`let` dec `=` `bitfield_rle``::`decode`(`enc`)``;`
`let` bits `=` `Bitfield``::`from_bytes`(`dec`)``;`
`assert_eq!``(`bits`.``get``(``400``)``,` `true``)``;`

## Format

The encoded bitfield is a series of compressed and uncompressed bit sequences. All sequences start with a header that is a varint.

If the last bit is set in the varint (it is an odd number) then a header represents a compressed bit sequence.

`S = varint([l << 2, b << 1, 1])
where
S = compressed sequence
l = byte length of sequence
b = bit
`

If the last bit is set to

then a header represents an uncompressed bit
sequence.`0`

`S = [varint([l << 1, 0]), b]
where
S = uncompressed sequence
l = byte length of bitfield
b = bitfield
`

## Installation

`$`` cargo add bitfield-rle`

## License

MIT OR Apache-2.0

#### Dependencies

~67KB