Struct chd::codecs::LzmaCodec

pub struct LzmaCodec { /* private fields */ }

Available on codec_api only.

LZMA (lzma) decompression codec.

Format Details

CHD compresses LZMA hunks without an xz stream header using the default compression settings for LZMA 19.0. These settings are

• Literal Context Bits (lc): 3
• Literal Position Bits (lp): 0
• Position Bits (pb): 2

The dictionary size is determined via the following algorithm with a level of 9, and a reduction size of hunk size.

fn get_lzma_dict_size(level: u32, reduce_size: u32) -> u32 {
    let mut dict_size = if level <= 5 {
        1 << (level * 2 + 14)
    } else if level <= 7 {
        1 << 25
    } else {
       1 << 26
    };

    // This does the same thing as LzmaEnc.c when determining dict_size
    if dict_size > reduce_size {
        for i in 11..=30 {
            if reduce_size <= (2u32 << i) {
                dict_size = 2u32 << i;
                break;
            }
            if reduce_size <= (3u32 << i) {
                dict_size = 3u32 << i;
                break;
            }
        }
    }
    dict_size
}

Buffer Restrictions

Each compressed LZMA hunk decompresses to a hunk-sized chunk. The input buffer must contain exactly enough data to fill the output buffer when decompressed.

Trait Implementations

impl CodecImplementation for LzmaCodec

fn new(hunk_size: u32) -> Result<Self>

Creates a new instance of this codec for the provided hunk size.

fn decompress( &mut self, input: &[u8], output: &mut [u8] ) -> Result<DecompressResult>

Decompress compressed bytes from the input buffer into the output buffer.

impl CompressionCodecType for LzmaCodec

fn codec_type(&self) -> CodecType

where Self: Sized,

Returns the known CodecType that this codec implements.

impl CompressionCodec for LzmaCodec