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add module doc comment

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Gered 2022-12-30 11:47:28 -05:00
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libretrogd/src/utils/lzw.rs
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//! GIF-variant implementation of LZW (Lempel-Ziv-Welch) compression and decompression.
//!
//! The GIF-specific changes/limitations from other LZW implementations are:
//!
//! * LZW-encoded data is packed into a series of one or more sub-chunks of data which are blocks
//! of at most 256 bytes in size, with the first byte of each chunk indicating the size of that
//! chunk (limited to 255 maximum, because it's only one byte). The sequence of sub-chunks is
//! terminated with a zero byte.
//! * Variable/dynamic code bit sizes are used. The minimum bit size supported is 2, while the
//! maximum bit size is 12, after which the code table will be reset before encoding/decoding
//! resumes.
//! * The input "minimum_code_size" parameter for both encoding and decoding must be a bit size
//! between 2 and 8.
//! * Internally the code table is always initialized with 256 entries for each byte value, and
//! then two extra special code values are added which are used by the GIF encoding process,
//! a "clear code" and an "end of information" code.
//! * The LZW-encoded stream always starts with a "clear code" and ends with an "end of information"
//! code. The "clear code" may also appear at other times within the stream.
use std::collections::HashMap;
use byteorder::{ReadBytesExt, WriteBytesExt};