Provided by: nspark_1.7.8B2+git20210317.cb30779-2_amd64 
NAME
spark - Archive file format for RISC OS version of the PC archiver Arc
CONVENTIONS
Strings are given in ASCII with C-style escapes. No terminating is present if not explicitily included.
Words are 32 bit little-endian numbers.
Half words are 16 bit little-endian numbers.
FORMAT
An archive file consists of a sequence of archive marker, archive header and file data, ie. marker1,
header1, data1, marker2, header2, data2, etc. The archive marker is a single byte of value 0x1a (26).
The archive finishes with an archive marker followed by a zero byte.
Header version number
This tells you how the file data is stored and how many bytes there are in the header. The header version
numbers for the PC, are detailed below. An Archimedes header version number is identical to the
corresponding PC number except it has bit 7 set.
1 Old style, no compression
2 New style, no compression
3 Compression of repeated characters only (RLE)
4 As 3 plus Huffman Squeezing
5 Lempel-Ziv packing of repeated strings (old style)
6 Lempel-Ziv packing of repeated strings (new style)
7 Lempel-Ziv Welch packing with improved hash function
8 Dynamic Lempel-Ziv packing with adaptive reset
9 PKARC style squashing
127 Un*x compression
Filename
14 bytes of name, zero terminated.
Compressed length
Compressed data length, one word.
Date
One half-word, date.
year = (date >> 9) & 0x7f;
month = (date >> 5) & 0x0f;
day = date & 0x1f;
Time
One half-word, time.
hour = (time >> 11) & 0x1f;
minute = (time >> 5) & 0x3f;
second = (time & 0x1f) * 2;
The time and date fields are always filled in. If the file has a load and exec address, these are the
time and date when the file was added to the archive otherwise, they are derived from the Archimedes
datestamp. In all extract operations on Archimedes format archives, the contents of the load and exec
fields take precedence.
CRC
One half-word, Cyclic Redundancy Check.
Original file length
Original file length, one word, only present if header type greater than 1.
Load address
Load address of the file, one word, only present if bit-7 of the header version number is set.
Exec address
Exec address of the file, one word, only present if bit-7 of the header version number is set.
Attributes
Attributes of the file, one word, only present if bit-7 of the header version number is set.
Compressed data...
Directories are stored as non-compressed archives within archives, ie. their load address &
0xffffff00=0xfffddc.
COMPATIBILITY
PC and Archimedes formats may be mixed in one archive for use on the Archimedes.
SEE ALSO
arcfs(5), nspark(1) SPARK(5)()