Re: flags in a bitmap

["Ruud H.G. van Tol" <rvtol@isolution.nl>]

On 2025-07-04 16:57, Ruud H.G. van Tol wrote:
> On 2025-07-04 16:16, Ruud H.G. van Tol wrote:
> > [switched from user to dev]
> >
> > On 2025-07-04 15:51, Bill Allombert wrote:
> > > On Fri, Jul 04, 2025 at 12:38:59PM +0200, Ruud H.G. van Tol wrote:
> > > > > ? install(bitset,vWL)
> > > > > ? x=2^(2^20);
> > > > > ? forprime(p=2,2^20,bitset(~x,p))
> > > > >     ***   last result computed in 8 ms.
> > > > > ? my(S=0);for(i=0,2^20-1,S+=bittest(x,i));S
> > > > > %16 = 82025
> > > > >     ***   last result computed in 159 ms.
> > > > That indeed looks good, and I can test it.
> > > Great, I have made a GIT branch bill-bitset
> > >
> > > commit 8632eaf7528554234aaa90d9a503476452cbd736 (HEAD -> 
> > > bill-bitset, origin/bill-bitset, master)
> > > Author: Bill Allombert <Bill.Allombert@math.u-bordeaux.fr>
> > > Date:   Thu Jul 3 23:57:00 2025 +0200
> > >
> > >      New GP functions bitset, bitclear
> >
> > Thanks. First (minor) remark:
> >
> >
> > -Help: bitclear(~n,i): clear bit i of n (in place)
> > +Help: bitclear(~x,n): clear bit n of x (in place)
> >
> > -Help: bitset(~n,i): set bit i of n in place
> > +Help: bitset(~x,n): set bit n of x in place
> >
> >
> > to align it with bittest, and with the code.
>
> And of course another:
>
> diff --git a/src/headers/paridecl.h b/src/headers/paridecl.h
> +void    bitclear(GEN x, long i);
> +void    bitset(GEN x, long i);
>  long    bittest(GEN x, long n);
>
> Those long i's might also want to be n's.

These 3 are less equally worded than I would expect:

-Help: bitclear(~x,n): clear bit n of x (in place)
=Help: bitflip(~x,n): flip bit n of x in place, assuming x >= 2^n.
-Help: bitset(~x,n): set bit n of x in place, assuming x>=2^n.

+Help: bitclear(~x,n): clear bit n of x in place, assuming x >= 2^n.
=Help: bitflip(~x,n): flip bit n of x in place, assuming x >= 2^n.
+Help: bitset(~x,n): set bit n of x in place, assuming x >= 2^n.


This looks special to me:

? my(x=2^4); print(x); bitclear(x,4); print(x);
16
Vecsmall([])

? my(x=2^4); print(x); bitflip(x,4); print(x);
16
Vecsmall([])

as I expected 0.

-- Ruud