Re: portable way to get highest bit set?

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From	Ian C <deathstation9000@gmail.com>
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Subject	Re: portable way to get highest bit set?
Date	Wed, 11 Oct 2023 18:03:38 +0100
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On 11/10/2023 17:19, candycanearter07 wrote:
> On 10/11/23 02:27, Anton Shepelev wrote:
>> candycanearter07:
>>
>>> What is the best/most portable way to get the highest bit
>>> set?
>>>
>>> ie. 011010001
>>> to  010000000
>>
>> What is your best attempt, even if unsuccessful?
>>
> 
> int out;
> for(out = 0x100000000; out; out >> 1)
>      if(out & input) break;
> 
> I'm trying to find something size independent, though.
> Or at least able to be swapped out with a #define

If you want the highest bit, 0x800000000 may be a better start :-)

If it was me I'd do it in reverse.  Assuming it's unsigned, shift your 
input to the right until it hits zero, counting the number of shifts 
which will be your bit number.  Assuming my head is currently working.


Ian C

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Re: portable way to get highest bit set? candycanearter07 <no@thanks.net> - 2023-10-11 11:19 -0500
  Re: portable way to get highest bit set? David Brown <david.brown@hesbynett.no> - 2023-10-11 18:45 +0200
  Re: portable way to get highest bit set? Ian C <deathstation9000@gmail.com> - 2023-10-11 18:03 +0100
    Re: portable way to get highest bit set? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-10-11 10:17 -0700
  Re: portable way to get highest bit set? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-10-11 10:34 -0700
  Re: portable way to get highest bit set? Richard Harnden <richard.nospam@gmail.invalid> - 2023-10-11 19:02 +0100

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