One thing to consider if you are planing on doing this in C on CP/M-80 is
that the executable for LU310 is already 20k. If you are going to add
code for LZH compression/decompression and date support you may not have
much memory left for actually processing the archive and handling the
memory needed for the compression/decompression routine. One option you
might want to consider is using external programs. There was an
archiving tool for LBR files that allowed you to integrate external
programs to do this but unfortunately I can't remember the name.
Other than that if you haven't seen it before there is a program called
LT v31 on the Walnut Creek CD that can can extract and view files in
a .LBR archive. It is only 7Kb and handles LHA compressed member files
as well as those compressed with Squeeze and Crunch.
It is available here:
http://cpmarchives.classiccmp.org/cpm/Software/WalnutCD/beehive/compress/lt31.lbr
Best wishes
Lorry
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Word Processors on the Commodore VIC-20
https://techtinkering.com/articles/word-processors-on-the-commodore-vic-20/