The Earliest Unix Code: An Anniversary Source Code Release

Re:The Earliest Unix Code: An Anniversary Source Code Release by kazinator on Thursday October 17, 2019 @07:22PM (#21287272)

If dotdot can't be opened it fails. So I don't think creat was the same as what we now know.

It looks like the code opens dotdot, and then scans through it for something (match for dir?).

The creat call might mean "open for writing", and possibly the flags mean append. It appears dir is appended to the dotdot directory file.

So maybe, add this "dir" entry to dotdot if it isn't there already?

I can't guess what initializes dir; maybe it somehow comes as an argument from the command line or whatever.

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Re:The Earliest Unix Code: An Anniversary Source Code Release by Pete_D on Thursday October 17, 2019 @08:10PM (#21287517)

dir appears to be copied into from tbuf at some point. It puts dir-1 into memory location 8 at the start, and then the code around the 2: section I'm pretty sure is a memcpy-ish loop like:

    c1 = -8;
    *9 = tbuf - 1;
    do {
        *(++(*8)) = *(++(*9));
    } while(++c1 != 0);
    goto 1b; // b for backwards?

It seems that memory locations 8-15 are auto-indexing[0], so the lac/dac i increments the pointed-at location before use, and isz is "increment and skip next instruction if zero".

[0] PDP7 manual, big PDF: http://bitsavers.trailing-edge.com/pdf/dec/pdp7/F-75P_PDP7pr...

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