Found it. A long read, but interesting. http://anubis.dkuug.dk/JTC1/SC22/WG14/www/docs/n972.pdf.
To give credit where it is due, Bill Seymour sent me the URL back in August of last year. (Guess is was only 6 months ago I was doing this.) ----- Original Message ----- From: "Stephen Nutt" <[EMAIL PROTECTED]> To: "Boost mailing list" <[EMAIL PROTECTED]> Sent: Friday, February 28, 2003 7:48 PM Subject: Re: [boost] Is there any Interest in a Fixed Point Library? > Kevin, > > I started on this must be close to a year ago, and I got wrapped up with > other stuff and never got back to it. > > A couple of interesting design ideas. Someone (sorry I forget who) pointed > me towards a great pdf file describing a fixed point arithmetic enhancement > for embedded compilers. It was very cool, and had some great ideas. > > One nifty option was to specify what would happen on overflow. There were > two choices. Either the number would not overflow but go to its limit, or > it would overflow in the 'expected' way. (Did that make sense?) > > So if I had a class > fixed<unsigned char, 3> a = 3.0; // 8 bit fixed point number with three > significant bits > > a * 3 would either give me 7.96875 or 1.0 A possible third choice would be > to raise an exception on overflow/underflow. > > My personal interest in the template was for a highly efficient 64 bit fixed > point number. As it turned out, there was no 64 bit support in Boost at the > time, and getting it turned out to be more of a pain than I had time for! > It may be there now as I think I've seen others look for this also since. > > I put together some great templates so I could do arithmetic like > > fixed <int, 6> a = val1; > fixed <char, 3> b = val2; > fixed <long, 9> = a + b; > > without loss of precision. > > I also have templates to do 64 bit arbitary fractional multiplication and > division without loss of precision. I also have a 64 bit squareroot > function lurking somewhere in the depths of my harddrive. I'm not sure how > all of this would work if the type was say complex, but I'm sure it could be > worked on. > > I'll look for the pdf I mentioned above and if I find it I'll post a url. I > think this is a great place to start as I believe there is a reasonable > demand for fixed point arithemetic in embedded computers. > > Stephen > > ----- Original Message ----- > From: "Kevin Atkinson" <[EMAIL PROTECTED]> > To: "Boost mailing list" <[EMAIL PROTECTED]> > Sent: Wednesday, February 26, 2003 9:28 PM > Subject: [boost] Is there any Interest in a Fixed Point Library? > > > > > > Is there any interest in a fixed point math library. Using templates the > > compiler can keep track of the radix point for you making using fixed > > point math a lot less tedious and error prone. > > > > Attached is a rudimentary implementation which would work acceptably when > > the exponent is not too large or too small. If the exponent is smaller or > > larger than the size of the underlying integer in bits this code will > > likely behave badly. > > > > I plan to use the attached code to avoid having to deal with serializing > > floating point numbers. A exponent of -30 (-31 if using an unsigned 32 > > bit integer) is especially useful for representing numbers between 0 and > > 1. The precision will actually be a bit better than a 32 bit float since > > the exponent does not have to be stored. > > > > Comments on the code welcome. I am not a numerical analysis specialist so > > don't expect me to write a fixed point library for anything beyond simple > > arithmetic. > > > > -- > > http://kevin.atkinson.dhs.org > > > > > -------------------------------------------------------------------------- -- > ---- > > > > _______________________________________________ > > Unsubscribe & other changes: > http://lists.boost.org/mailman/listinfo.cgi/boost > > > _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
