Author: Russell Reagan
Date: 20:30:50 12/03/02
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On December 03, 2002 at 15:50:15, Russell Reagan wrote:
>bsf: 4.265 seconds
>LSB_64: 42.968 seconds
>LastOne(): 39.906 seconds
>FirstOne(): 55.125 seconds
I was just fooling around and wrote this one. It finished in 41.250 seconds.
const int high_one_8bit[256] = {
-1,0,1,1,2,2,2,2,3,3,3,3,3,3,3,3,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,5,5,5,5,5,
5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,6,6,6,6,6,6,6,6,6,6,
6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7
};
int high_one_c (boardmap_t _bits)
{
int offset;
int result;
result = (_bits > 0xffffffff) * 32;
unsigned int bits = _bits >> result;
offset = (bits > 0xffff) * 16;
bits >>= offset;
result += offset;
offset = (bits > 0xff) * 8;
bits >>= offset;
result += offset;
return result + high_one_8bit[bits];
}
Perhaps there is some additional optimization that can be done here. I just
thought this up real quick. The idea is to get rid of the 64-bit value as soon
as possible so the rest will run faster on a 32-bit machine. No match for bsf on
the pentium though.
Maybe we could start a collection of these, with times and everything for
different processors. I think it would be some interesting data to see all of
these different algorithms and their results on various processors (athlon, p3,
p4, hammer, itanium, etc.). Maybe I'll start collecting, although Gerd probably
has a great collection going so far :)
Russell
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