Xref: utzoo comp.arch:17585 comp.databases:6735 Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!ucsd!network.ucsd.edu!celit!dave From: dave@fps.com (Dave Smith) Newsgroups: comp.arch,comp.databases Subject: Re: Extremely Fast Filesystems Keywords: addressing,fractions,floating-point,caches Message-ID: <10641@celit.fps.com> Date: 8 Aug 90 02:30:28 GMT References: <5539@darkstar.ucsc.edu> <13285@yunexus.YorkU.CA> <30728@super.ORG> <13667@cbmvax.commodore.com> <13578@yunexus.YorkU.CA> Sender: daemon@fps.com Reply-To: dave@fps.com (Dave Smith) Followup-To: comp.arch Organization: FPS Computing Inc., San Diego CA Lines: 26 In article rbw00@JUTS.ccc.amdahl.com ( 213 Richard Wilmot) writes: >I still think it is time to stop trying to use integers for addressing. >They always break down and probably always will. Many computers today have >floating point units. I would like to see floating point used for addressing. >It would help a great deal if addresses were not dense. What I have in mind >is for data objects to have addresses but these would be floating point and >between any two objects we could *always* fit another new object. This won't work. There are only so many distinct numbers representable by floating point. There will be points where there is no "room" between two numbers because the granularity of the floating point doesn't allow a number to be represented between them. As a simple example with two digit decimal floating point (two digits of mantissa, one digit of exponent), find the number between 1.01x10^1 and 1.02x10^1. With a 64-bit (combined mantissa and exponent) floating point number there are 2^64 distinct numbers that can be represented. The range is very large, but the numbers are sparse. I liked the idea of "tumblers" as put forth by the Xanadu project. Variable length indices, that's the only way to go. I think I'll go over and hit the hardware engineers over the head until they figure out a way to make it fast :-). -- David L. Smith FPS Computing, San Diego ucsd!celerity!dave or dave@fps.com