Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!elroy.jpl.nasa.gov!ncar!gatech!ukma!usenet.ins.cwru.edu!agate!sprite.berkeley.edu!shirriff From: shirriff@sprite.berkeley.edu (Ken Shirriff) Newsgroups: sci.electronics Subject: Re: VCR PLUS+ ...PSSST...WHAT'S THE CODE? Keywords: encoding Message-ID: <1991May6.200411.2847@agate.berkeley.edu> Date: 6 May 91 20:04:11 GMT References: <4764@osc.COM> <1991May6.165343.5041@msuinfo.cl.msu.edu> Sender: root@agate.berkeley.edu (Charlie Root) Distribution: usa Organization: University of California, Berkeley Lines: 29 In article <1991May6.165343.5041@msuinfo.cl.msu.edu> mackay@eecae.ee.msu.edu (James F. MacKay) writes: >Has anyone considered how much information is in this short code? I've >tried a few encoding schemes that I might use in designing a code and >can't seem to figure out how they put so much info in so little space. The trick is they use variable length codes. Common things are short and uncommon things are long (kind of like Huffman encoding.) Assuming normal shows start on half hours and are 30, 60, or 90 minutes long and there are 50 channels and 7 days gives us 48x3x50x7=50400 possibilities. This matches the common numbers being about 4-5 digits long. Also, low channel numbers seem to have shorter codes than high channel numbers. On the other hand movies that, for example, start at 3:14 and go 98 minutes have long codes of about 10 digits. Assuming shows start any time during the day and go less than 24 hours on 100 channels gives us 24x60x24x60x100x7= 1.4x10^9 which fits in 10 digits. So there seems to be a short code for typical shows and a long code for arbitrary shows. I don't know if there are 2 codes, or more in between, or the same code varying in length somehow. Disclaimer: this is based on a few minutes of examining the numbers in the tv guide. So I may be wrong. P.S. Has anyone asked sci.crypt if they have ideas? Ken Shirriff shirriff@sprite.Berkeley.EDU