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- To: <firstname.lastname@example.org>, <email@example.com>
- Subject: Re: floats
- From: firstname.lastname@example.org
- Date: Wed, 19 Nov 97 11:31:11 -0500
- Return-receipt-to: <email@example.com>
1. I do set *read-default-float-format* = double-float. The numbers
are still read as singles.
2. ~// in format is a luxury. single+float=single is a *MAJOR* *bug*.
People who wrote ANSI CL standard are not idiots. They had something
in mind -- correct computations, to be sure. (I am trying hard to
contain my emotions. Sorry.) You are trading *correct* result for
pretty-looking result. This is unbelievable!!!!!!!!!!!!!!!
To use your impnotes example: "(- (+ 1.7 pi) pi) should not return
1.700000726342836417234L0," This 1.700000whatever is still 1.7, for
purposes of practical computations. But when I am getting *negative*
standard deviations, this is not correct in any possible sense!!!!
Single for 1.123 is OK, but when I take squares etc., it stops being
OK!! I know that and I want to use doubles because of that!
You think that a float is always imprecise. You are *wrong*. 123456.7
is *precise*, and I should not have to use ratios to tell clisp that!
And if I want to compute the square, I want it to be precise too.
Anyway, can you name another computer system where
I just can't believe this could ever happen!
I am sorry, it is kind of hard to remain calm when encountering
something like this.
______________________________ Reply Separator _________________________________
Subject: Re: floats
Author: <firstname.lastname@example.org> at INET
Date: 1997-11-19 22:42
Sam Steingold <email@example.com> writes:
> I am having a *very* nasty problem. I want all my floats to be double.
> Always. I set *default-float-format* to 'double-float, *and* set the
> vars as 0.0d0. And still end up with numbers like 644151.75f0.
When you read floats from files, you also need to have
*read-default-float-format* = double-float.
> This can be traced to
> > (+ 0.0d0 1233456.2345f0)
> which is quite outrageous, since *I* would expect it to be double on
> the grounds of double + single = double no matter what! :-)
This is a different issue: Once your data is already infected with
single-floats, does this disease spread or not? In ANSI CL compliant
systems, the double-floats take over again but inaccuracies spread
nevertheless under cover. In CLISP, with the rule "double + single = single",
the single-floats spread, so it's easier for you to detect them.
For more explanations, see section 12.1. of