bug in (log)

[Stas Boukarev]

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http://www.lispworks.com/documentation/HyperSpec/Body/12_acc.htm

On Sun, Jul 3, 2022 at 12:10 AM James Cloos <cloos at jhcloos.com> wrote:
>
> (gitlab is uusable; i have to report here.)
>
> ecl 21.2.1 gives:
>
> > (log 1/6319748715279270675921934218987893281199411530039296)
>
> Debugger received error of type: DIVISION-BY-ZERO
> #<a DIVISION-BY-ZERO 0x7ff5afe6c540>
> Error flushed.
>
> whereas other cl's (i testyed sbcl and ccl) give results like:
>
> ? (log 1/6319748715279270675921934218987893281199411530039296)
> -119.27552
>
> I tested on amd64 (gentoo) and arm64 (debian and netbsd) with identical
> results.  i did not have a musl box or other bsd to test on.
>
> run with --no-trap-fpe, the result is #<single-float negative infinity>.
>
> another example is:
>
> (truncate (log 1/6319748715279270675921934218987893281199418867))
>
> Debugger received error of type: ARITHMETIC-ERROR
> #<a ARITHMETIC-ERROR 0xffff8f688a40>
>
> whereas this works:
>
> (truncate (log 1/631974871527927067592193421898789328119941867))
>
> -103
> -0.27893066
>
> which of course suggests that the issue is c's long double's precision.
>
> it looks like ecl could use an mpq log function;
> https://github.com/linas/anant might work.
>
> -JimC
> --
> James Cloos <cloos at jhcloos.com>         OpenPGP: 0x997A9F17ED7DAEA6
>