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57 lines
1.3 KiB
Plaintext
57 lines
1.3 KiB
Plaintext
About
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Text compression format that can be decompressed starting at any point.
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Little-endian byte ordering is used.
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Header
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------
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TCR files always start with:
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!!8-Bit!!
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Layout
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------
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Header
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256 key dictionary
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compressed text
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Dictionary
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----------
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A dictionary of key and replacement string. There are a total of 256 keys,
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0 - 255. Each string is preceded with one byte that represents the length of
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the string.
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Compressed text
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---------------
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The compressed text is a series of values 0-255 which correspond to a key and
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thus a string. Reassembling is replacing each key in the compressed text with
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its corresponding string.
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Compressor
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-----------------
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From Andrew Giddings TCR.c (http://www.cix.co.uk/~gidds/Software/TCR.html):
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The TCR compression format is easy to describe: after the fixed header is a
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dictionary of 256 strings, each preceded by a length byte. The rest of the
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file is a list of codes from this dictionary.
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The compressor works by starting with each code defined as itself. While
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there's an unused code, it finds the most common two-code combination, and
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creates a new code for it, replacing all occurrences in the text with the
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new code.
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It also searches for codes that are always followed by another, which it can
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merge, possibly freeing up some.
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