Re: [PATCH] rev-list: estimate number of bisection step left

[John Tapsell <johnflux@gmail.com>]

2009/2/17 Johannes Schindelin <Johannes.Schindelin@gmx.de>:
> Hi,
>
> On Tue, 17 Feb 2009, Christian Couder wrote:
>
>> +static int estimate_bisect_steps(int all)
>> +{
>> +     int log2 = 0;
>> +     int left = (all >> 1) - 1;
>> +
>> +     if (left <= 0)
>> +             return 0;
>> +
>> +     do {
>> +             left = left >> 1;
>> +             log2++;
>> +     } while (left);
>> +
>> +     return log2;
>> +}
>
> How about this instead, calling it from cmd_rev_list directly?
>
>        static int log2(int n)
>        {
>                int log2;
>
>                for (log2 = 0; n > 1; log2++)
>                        n >>= 1;
>
>                return log2;
>        }

This would work, if you want a non-iterative solution

unsigned int log2_integer_approximate(unsigned int n){
*((float*)&n) = (float)n;
return ((n & (~((1<<23) - 1))) >> 23) - 127;
}

(It's correct up to 2^25, then it's off by 1 for a few.)


> Ciao,
> Dscho
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