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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: portable way to get highest bit set?
Date: Wed, 11 Oct 2023 10:17:17 -0700
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Ian C <deathstation9000@gmail.com> writes:

> 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.

Wouldn't you first write a test function to be sure the
value returned is correct?  ;)

I found it harder to write a correct test function than
to write a function that just returns a correct value.
Interesting, eh?