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Re: arithmetic issues
| Date: Fri, 21 Oct 2005 11:59:06 -0400
| From: "John.Cowan" <jcowan@xxxxxxxxxxxxxxxxx>
| Aubrey Jaffer scripsit:
| > For an interpreter this would mean that 1/2 read before the
| > full-tower module was loaded could be an inexact 0.5; but after
| > loading 1/2 would read as an exact 1/2. Unpredictability is bad.
| It would merely mean that 1/2 would be an error (and preferably
| would signal an error as well). Of course, #e1/2 would still be an
| inexact 0.5.
I think you meant #i1/2
| > None of the examples in SRFI-77 return -0.0 unless they are
| > passed -0.0 as an argument. Does -0.0 result only from a literal
| > -0.0 constant?
| > In an implementation with -0.0, what is the result of (* -5.0 0.0)?
| > -0.0 is insufficiently specified by SRFI-77; it will be a portability
| > killer.
| The IEEE standard is our friend here.
0.0 being the most common inexact number, SCM has only one boxed 0.0.
Thus in SCM:
(/ (* 0.0 -5.0)) ==> +inf.0
While in an implementation with two zeros:
(/ (* 0.0 -5.0)) ==> -inf.0
Thus dual zero systems behave differently from single zero systems,
which can cause portability problems.