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Bill Allombert on Sat, 14 Sep 2024 12:49:29 +0200
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Re: A missing (?) function: exponentfp(x)
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- To: pari-dev@pari.math.u-bordeaux.fr
- Subject: Re: A missing (?) function: exponentfp(x)
- From: Bill Allombert <Bill.Allombert@math.u-bordeaux.fr>
- Date: Sat, 14 Sep 2024 12:49:25 +0200
- Delivery-date: Sat, 14 Sep 2024 12:49:29 +0200
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- References: <ZuVStcuY1kXNpxs6@debian.attlocal.net> <ZuVYiLiVUwtZQKGd@seventeen> <CAMLkfFQOzvh9+dnqX4yUQeM_wU=HHiqKM3sNTUGC1wW821p6Cg@mail.gmail.com>
On Sat, Sep 14, 2024 at 12:31:57PM +0200, Loïc Grenié wrote:
> In gp you can cheat
>
> ? install(dbllog2,lG);
> ? install(dbltor,L);
> ? flog2(x)=dbltor(dbllog2(x));
It is not robust because the calling convention put double in different
registers than long so dbltor would not find its input.
However it can work by luck if the value stay in the floating point registers:
? a=dbllog2(Pi); dbltor(a)
%13 = 0.E-307
? dbltor(dbllog2(Pi))
%14 = 1.6514961294723207175
But then you can as well do:
install(dbllog2,vG);
install(dbltor,"");
flog2(x)=dbllog2(x);dbltor();
flog2(Pi)
%10 = 1.6514961294723207175
Cheers,
Bill.