Re: [PATCH 1/2] factor: add option for printing in x^y format

[Bernhard Voelker]

On 4/27/22 16:14, Pádraig Brady wrote:
> On 27/04/2022 11:07, Rasmus Villemoes wrote:
>> When factoring numbers that have a large 2^n factor, it can be hard to
>> eyeball just how many 2's there are. Add an option to print each prime
>> power factor in the x^y format (omitting the exponent when it is 1).
>>
>> * src/factor.c: Add --exponents option for printing in x^y format.
>>
>> Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
> 
> Thanks for the suggestion.
> This is one of those borderline cases.
> 
> Mainly because it's fairly easy to postprocess the output.
> Consider for example:
> 
>    $ factor 13 36 | tr ' ' '\n' | uniq -c
>          1 13:
>          1 13
>          1 36:
>          2 2
>          2 3
> 
> Though for interactive use, the new option is a benefit.
> 
> Given the interactive benefit and a previous request to add this 
> functionality¹
> I'm tentatively leaning towards adding this.
> 
> cheers,
> Pádraig
> 
> ¹ https://lists.gnu.org/archive/html/coreutils/2017-11/msg00015.html

Regarding the postprocess solution:
this is a little awk(1) snippet to get the same output as with the patch:

  $ factor 13 36 | tr ' ' '\n' | uniq -c | awk '\
      BEGIN { n="" }
      /:$/  { printf("%s%s", n, $2); n="\n"; next };
            { printf(" %s%s", $2, ($1>1?"^"$1:"")); }
      END   {printf("%s",n); }
      '
  13: 13
  36: 2^2 3^2

Re. the patch:
the implementation is quite clean in 2 places - the LONGINT_OK and the MPZ case 
- and
doesn't seem to get into the way of any future extensions (null-separated 
output, whatever).

Therefore, I'm also 70:30 for adding it.
Of course, we'd also need a long option and texinfo documentation.

Finally, regarding '-e': is there any precedence (or a clashing option) in any 
other
factor(1) implementation?

Have a nice day,
Berny