Am 16.04.2011 um 23:03 schrieb Ralf Hemmecke:
> On 04/16/2011 10:04 PM, Prof. Dr. Johannes Grabmeier wrote:
>> can anybody explain the meaning of the length function in Integer? I
>> thought that should be the length of the binary expansion, at least
>> for i>= 0:
>
> Thank you for reporting.
>
> I consider this a bug.
that is what I think as well, but I disagree with your "solution" to fix only
the documentation, not the bug on which we agree!
>
> In integer.spad the implementation is:
>
> length a == INTEGER_-LENGTH(a)$Lisp
>
> whereas its definition is in si.spad (IntegerNumberSystem).
>
> length : % -> %
> ++ length(a) length of \spad{a} in digits.
We should fix this to
++ length(a) length of \spad{a} in binary digits neglecting a negative
sign
length(-8) should return 4
>
> Very clear this is. :-( What is a digit? Binary digit? Decimal digit?
> Since that is not clearly defined, the implementation could even return
> something else.
>
> And the implementation via integer-length is maybe not perfectly representing
> what one would intuitively understand by "lenght in digits".
> http://www.cs.utexas.edu/users/moore/acl2/v4-2/INTEGER-LENGTH.html
>
> I've somehow the impression that even the lisp documentation is wrong. I
> would believe that representing 0 requires at least 1 bit, but it's probably
> a question of making the specification one way or the other. So, it would be
> better to explicitly define length(0)=0.
>
> So my suggestion would be to fix the documentation rather than the code.
> Other opinions?
>
> While we are at it... anybody else experiencing a crashing hyperdoc?
>
> Click Browse
> Enter "lenght"
> click "Operations"
> Click "Signatures"
> Click on the 4th "lenght"
>
> My HyperDoc window disappears.
>
> Ralf
>
>
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Mit freundlichen Grüßen
Johannes Grabmeier
Prof. Dr. Johannes Grabmeier
Köckstraße 1, D-94469 Deggendorf
Tel. +49-(0)-991-2979584, Tel. +49-(0)-171-5503789
Tel. +49-(0)-991-3615-100 (d), Fax: +49-(0)-1803-5518-17745
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