Squash (RISC OS)
Contents |
Overview
Squash files (file type FCA, Squash) contain compressed data for single files on RISC OS systems.
The file command calls this format "squished".
Format
According to the help text for the Squash application, "The Squash module currently compresses using a 12-bit LZW algorithm but no guarantee is made that this will be so in the future."
The compressed data is preceded by a header, with offsets measured in bytes and all values stored in little-endian byte order:
| Offset | Description |
|---|---|
| 0 | "SQSH" (4 byte ID) |
| 4 | Length of the original, uncompressed file in bytes |
| 8 | Load address of the original file |
| 12 | Execution address of the original file |
| 16 | Reserved (should be 0) |
As with a number of data formats related to filing systems on RISC OS, the load and execution addresses are actually used to hold the file type and date stamp of the original file.
The remaining data in the file (from offset 20 to the end) can be decompressed using gunzip. One way to do this is to run the following in a bash shell:
dd if=input_file skip=20 bs=1 | gunzip -c - > output_file
Sample files
References
- Help file for the Squash application
- Manual page in the RISC OS 3.7 user guide
- The Unofficial Acorn Filetypes List
