Provided by: nspark_1.7.8B2+git20210317.cb30779-2_amd64
spark - Archive file format for RISC OS version of the PC archiver Arc
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.
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.
PC and Archimedes formats may be mixed in one archive for use on the Archimedes.