A question on the range of floats in Emacs

A question on the range of floats in Emacs

[Jay Belanger]

The Elisp manual says that the range of integers depends on the
machine, but the information is available within Emacs
(most-positive-fixnum, etc.), and what's more there is a minimum range.
The range of floating points also depends on the machine.  I'm
wondering:
  Is the precise range easily available from within Emacs?
  Is there a minimum range?

Thanks,
Jay

Re: A question on the range of floats in Emacs

[Johan Bockgård]

Jay Belanger <jay.p.belanger@gmail.com> writes:

> The Elisp manual says that the range of integers depends on the
> machine, but the information is available within Emacs
> (most-positive-fixnum, etc.), and what's more there is a minimum range.
> The range of floating points also depends on the machine.  I'm
> wondering:
>   Is the precise range easily available from within Emacs?
>   Is there a minimum range?

The cl package can determine a number of floating point parameters.
See

  (info "(cl)Implementation Parameters")

-- 
Johan Bockgård

Re: A question on the range of floats in Emacs

[Jay Belanger]

bojohan+news@dd.chalmers.se (Johan Bockgård) writes:
...
> The cl package can determine a number of floating point parameters.
> See
>
>   (info "(cl)Implementation Parameters")

Wonderful; thanks.
I guess this information isn't easily accessible, so it is 
computed.  I played around with the largest and smallest floats, and I
was wondering about precision.  Near the smallest float, the precision
can be small; on my computer, 5e-324, 5.1e-324 and 4.9e-324 all evaluate to
5e-324; 3.47e-323 evaluates to 3.5e-324, etc.  Is there a range (say
from smallest-exponent + N to largest-exponent - N) in which the
precision is fixed?  (It appears that way here; is it true in general?)

Jay

Re: A question on the range of floats in Emacs

[Eli Zaretskii]

> From: Jay Belanger <jay.p.belanger@gmail.com>
> Date: Tue, 17 Jul 2007 15:41:12 -0500
> Cc: jay.p.belanger@gmail.com
> 
> I played around with the largest and smallest floats, and I
> was wondering about precision.  Near the smallest float, the precision
> can be small; on my computer, 5e-324, 5.1e-324 and 4.9e-324 all evaluate to
> 5e-324; 3.47e-323 evaluates to 3.5e-324, etc.  Is there a range (say
> from smallest-exponent + N to largest-exponent - N) in which the
> precision is fixed?  (It appears that way here; is it true in general?)

The numbers where you see the loss of precision are denormalized
(i.e. some of the mantissa bits are zero).  The range you are looking
for (where there's no loss of precision) is between
least-positive-normalized-float and most-positive-float.

Re: A question on the range of floats in Emacs

[Jay Belanger]

Eli Zaretskii <eliz@gnu.org> writes:
...
> The numbers where you see the loss of precision are denormalized
> (i.e. some of the mantissa bits are zero).  The range you are looking
> for (where there's no loss of precision) is between
> least-positive-normalized-float and most-positive-float.

Thanks!

Jay