💩 On Nov 9, 2015 6:09 PM, "Clem Cole" wrote: > Outstanding. I love it. You can use emoji's today and have the > scatological references inline. > > Clem > > On Mon, Nov 9, 2015 at 6:49 PM, Marc Rochkind > wrote: > >> Since you asked, here's the true story of how I came up with the delta >> encoding, a story never before told. >> >> I was living in a garden apartment in Sayreville, NJ, and at night would >> walk my girlfriend's dog along a hillside just outside our front door. It >> was usually cold, I didn't like the dog (still don't like dogs), and hated >> dodging the piles of dog shit while he tugged on the leash. So, as a coping >> mechanism, I used to let my mind wander, and one evening it was wandering >> and wondering about a problem I was struggling with, which was how to store >> the source and the deltas all in the same file. (It was a "data set," on >> the IBM OS/360 system we were using--we weren't on UNIX yet.) >> >> Anyway, no doubt simultaneously with this unpleasant animal taking a >> shit, I came up with idea of surrounding pieces of text with markers. (The >> algorithm itself is documented in my original 1975 paper, which you can >> read about here: http://basepath.com/aup/talks/SCCS-Slideshow.pdf.) >> >> (Wouldn't this be an even better story if I said that the little piles of >> dog poop on the hillside looked like markers in the soft glow of a full >> moon? It's not true, but perhaps I'll tell it that way if the occasion >> arises in the future.) >> >> When I got inside, I started to sketch out how the markers might work, >> and came up with interesting observation that insertion start/end markers >> obviously nested, but deletion start/end markers did not nest with insert >> start/end markers. This is obvious if you think about it the right way: >> When you delete, the text you're deleting could have been added at various >> times, but when you insert, the inserted text is always added at the same >> time. >> >> I didn't have replacement markers; insert and delete were enough, I >> thought. >> >> I kept fooling around with the idea until I had an algorithm that I >> thought would work to retrieve any version with a single pass. (It's in the >> paper, referenced above.) >> >> To prove the algorithm to be correct, I enumerated all possible cases of >> insertions mixed in with deletions. I don't recall how many cases I had, >> but I think it was around 20 or 30. Then I painstakingly went though every >> case, making sure the algorithm produced the right answer. This was a rare >> example of me doing actual work. >> >> Coding it up, as I remember, was very easy, as the scheme is pretty >> simple. I'm sure I had it running in SNOBOL4 in a day or two. Redesigning >> SCCS in C for UNIX came maybe a year or so later, but the algorithm >> remained the same. >> >> Larry very kindly says: "SCCS has interleaved deltas. It's a brilliant >> design that has far far better performance than anything else out there." >> >> Maybe it was brilliant, but I can tell you that I was just trying to pass >> the time while that stupid dog did his business. >> >> --Marc >> >> On Mon, Nov 9, 2015 at 4:05 PM, Larry McVoy wrote: >> >>> On Mon, Nov 09, 2015 at 04:02:44PM -0700, Marc Rochkind wrote: >>> > I just got on this list today, and I see that Larry McVoy asks: >>> > >>> > "I wish Marc was on this list, be fun to chat." >>> > >>> > I'd be happy to chime in on SCCS or early PWB questions, to the extent >>> I >>> > remember anything. >>> >>> Awesome! How about a start of how you came up with the SCCS design, >>> in particular the interleaved delta format (we internally call it >>> "the weave")? >>> >> >> >> _______________________________________________ >> TUHS mailing list >> TUHS at minnie.tuhs.org >> https://minnie.tuhs.org/mailman/listinfo/tuhs >> >> > -------------- next part -------------- An HTML attachment was scrubbed... URL: