floating point precision

[djh -8 at 8- ccl.net]

Kahan's "paranoia" is an interesting program that determines
 epsilon,
 as well as a host of other parameters, and makes a judgement on the
 quality of the machine's fp design and implementation.  [It thoroughly
 pans Crays!]
 It's available from netlib.  Send mail to
     netlib -8 at 8- ornl.gov
     Subject: send index from paranoia
 to get an overview of paranoia and directions on how to get various
 language versions of the program.
 You have to be careful in determining epsilon with a simple program.
 The Intel coprocessors, for example, work in 80 bit extended format,
 so depending on your compiler, you may get an epsilon of 2 ** (-52)
 if values get stored to memory, or 2 ** (-63) if they do not!  The
 latter value isn't going to be achieved in most real programs.
 I think for all IEEE fp, appropriate values are 2 ** (-23) for single
                                                 2 ** (-52) for double
 --
 David J. Heisterberg		djh -8 at 8- ccl.net		We are NOT all
 The Ohio Supercomputer Center	djh -8 at 8- ohstpy.bitnet	Keynesians now.
 Columbus, Ohio  43212		ohstpy::djh