Re: [Chicken-users] read / write floats

[Kon Lovett]

On Aug 25, 2007, at 1:44 PM, Gábor Balázs wrote:

Hello,

I tried the following with chicken 2.6:

    (define v1 (/ 1 3))
    (call-with-output-file "try.dat"
                           (lambda (port)
                             (write v1 port)))
                           
    (define v2 (call-with-input-file "try.dat"
                                     (lambda (port)
                                       (read port))))
    (print "v1 = " v1)
    (print "v2 = " v2)
    (print (equal? v1 v2))
    (print (= v1 v2))
    (print (- v1 v2))

And the result was:

    v1 = 0.333333333333333
    v2 = 0.333333333333333
    #f
    #f
    3.33066907387547e-16

Is it a known bug?

Yes. See http://galinha.ucpel.tche.br/Deviations%20from%20the%20standard [6.6.4]

This is real "gotcha" in core Chicken. See the " numbers" egg.

$ csi

this is CHICKEN

Version 2.637 - macosx-unix-gnu-ppc - [ manyargs dload ptables extraslot applyhook autotools ]

(c)2000-2007 Felix L. Winkelmann

; loading /Users/klovett/.csirc ...

#;1> (use numbers)

; loading /usr/local/lib/chicken/1x/numbers.scm ...

; loading /usr/local/lib/chicken/1x/numbers-base.so ...

#;2> (define v1 (/ 1 3))

    (call-with-output-file "try.dat"

                           (lambda (port)

                             (write v1 port)))

                           

    (define v2 (call-with-input-file "try.dat"

                                     (lambda (port)

                                       (read port))))

    (print "v1 = " v1)

    (print "v2 = " v2)

    (print (equal? v1 v2))

    (print (= v1 v2))

    (print (- v1 v2)) #;3> #;4> #;5> v1 = 1/3

"v1 = "

#;6> v2 = 1/3

"v2 = "

#;7> #t

#t

#;8> #t

#t

#;9>

However , this only works because the 'v' values are exact! '(define v1 (exact->inexact (/ 1 3)))' still has the read/write invariance problem.

I tried to report this, but I did not find the easy way.

See http://trac.callcc.org/

`bg`

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