Re: bit_ffs

On 2023-03-30 20:09, Bill Allombert wrote:
> On Thu, Mar 30, 2023 at 07:02:34PM +0200, Ruud H.G. van Tol wrote:
>> Might be interesting to add:
>>
>> https://en.wikipedia.org/wiki/Find_first_set
>> https://www.man7.org/linux/man-pages/man3/ffs.3.html
>> https://www.go4expert.com/articles/builtin-gcc-functions-builtinclz-t29238/
>>
>> Or are those too low-level?
>>
>> bit_ffs, bit_ctz
> For the bitxxx functions family in GP,
> you can use valuation(x,2) (resp. logint(x,2))

Find first set bit:

bit_ffs(n) = valuation(n, 2)


Count trailing set bits:

bit_cts(n) = valuation(n+1, 2)

-- Ruud