23 Jun
2016
23 Jun
'16
7:50 a.m.
On Thu, Jun 23, 2016 at 4:31 PM, Paul Koning <paulkoning at comcast.net> wrote:
Another interesting aspect where people may not be aware of how much
variety existed is in the encoding of floating point numbers. IEEE
is now the standard, but PDP-11 users will remember the DEC format
which is a bit different. CDC and IBM were different still. The
Dutch machine Electrologica X8 had a particularly interesting
approach (parts of which were adopted, many years later, by the IEEE
standard).
DEC floating point is still very much around, as VAX floating point.
Alpha had both IEEE and VAX floating point, and compilers on VMS
defaults to VAX floating point. On Itanium CPU's, the chip only has
IEEE floating point, but VAX floating point formats are provided by
the OS, and many customers still compile their code to use VAX
floating point formats.
There are many, many varieties of floating point formats. This page
gives a nice overview: http://www.quadibloc.com/comp/cp0201.htm
Camiel.