A simple compression library with very low memory footprint.
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README.md

README.md

squish

by Andrew G. Crowell (Overkill / Bananattack)

A simple lossless data compression library with very low memory footprint.

  • Compress files of up to 64K. (Designed with embedded systems with 16-bit address space in mind.)
  • Libraries for C, D, JavaScript, 6502 and GBZ80.
  • Mixes simplistic compression algorithms that require very little intermediate state during decompression.

Specification

  • The squish compression format is a stream containing 0 or more sequences of the following data:
    <header> <payload>
  • Each header is an 8-bit byte that contains a 6-bit length component and a 2-bit command component:
    <header> = ((<command> & 3) << 6) | (<length> & 0x3F)
  • The payload format is determined by the command in the header:
    • raw = 0 - Sequence of uncompressed bytes of indicated length.
    • rle8 = 1 - Single byte, to be unpacked length times.
    • rle16 = 2 - Two-byte pattern, to be unpacked length times.
    • ref = 3 - Reference to data earlier in the unpacked stream, a two-byte value specifying an offset in bytes from the beginning of the stream. The amount of bytes being referenced is of the indicated length.
  • A header byte that has a length of zero is considered an end-of-file marker.

License

Copyright (c) 2013 Andrew G. Crowell (Overkill / Bananattack)
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
   notice, this list of conditions and the following disclaimer in the
   documentation and/or other materials provided with the distribution.
3. Neither the name of squish nor the names of its contributors may be
   used to endorse or promote products derived from this software without
   specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL SQUISH CONTRIBUTORS BE LIABLE FOR ANY
DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.