On Wed, Jul 13, 2011 at 11:27:48AM -0700, Colin D Bennett wrote: > On Wed, 13 Jul 2011 11:05:56 -0700 > Colin D Bennett <co...@gibibit.com> wrote: > > > On Wed, 13 Jul 2011 19:55:02 +0200 > > Gabriel Paubert <paub...@iram.es> wrote: > > > > > Great. As an astronomer, I really need to be able to define > > > my PCB in astronomical units and parsecs :-) > > > > You'll have to wait for 64-bit internal unit storage... > > (when metric internals [nm units] is implemented) > > Correcting myself: > 2**64 nm ≈ 0.123 AU > 2**128 nm ≈ (2.3×10**18) AU > > I guess 64-bit numbers won't do it for you!
The dynamic range of values you need for some modelling code in astronomy is, well, astronomical. 25 years ago, I had to move some scientific code from an IBM 370 mainframe to a VAX. The dynamic range of single and double precision on the nefarious IBM hexadecimal floating point was roughly 10^+/-76 (16^+/-64). The VAX could only reach 10^+/-38 (2^+/-128) in both single and double precision at the time (later they added the so called G-float format with an 11 bit exponent like IEEE). It turned out that I had to be very careful and scale several variables because otherwise I triggered overflows and underflows on the VAX. I must admit that I've never run into problems with IEEE double precision (10^+/-308). Regards, Gabriel _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user