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

2009/2/17 Johannes Schindelin [off-list ref]:

Hi,

On Tue, 17 Feb 2009, Christian Couder wrote:

quoted

+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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