[chbot] !!!!!!!! Choc fish challenge 2 !!!!!!!!!

[jimmy allen]

Hello Charles ,everyone

This is hard.
Here is my attempt

void *x = 0
void *j = &x

while(x[j] == j[x]){
       j++; x++;
 }

I thinking this would keep running until x equals ram end and an index
error would occur.

I don't have a clue if I am anywhere close to correct as I have racked
my brain for this one.

Jimmy




On 8/2/11, Michael Field <hamster at snap.net.nz> wrote:
> It it Tuesday 10pm and nobody has answered?
>
> I think function(x) returns the the first power of two that is greater
> than or equal to x.
>
> It works because the first "shift and or"  propagates  the First Set Bit
> (FSB) to bit(FSB-1)
> The second "shift and or" propagates bits(FSB) and bit(FSB-1) to
> bit(FSB-2) and and(FSB-3)
> The third "shift and or" propagates bit(FSB) through bit(FSB-3) to
> bits(FSB-4) through bits(FSB-7)
> .... and so on.
>
> The "x--" at the start makes sure that it returns "greater than or equal
> to" x. If you remove it you get the first power of two greater than x.
> e.g. function(256) will return 512.
>
> But I don't think it works if x > 2^31, as for f(0x80000001) the return
> value will be 0xFFFFFFFF+1 = 0 <?>.
>
> Without the "x++" on the return it would be quite handy to light a
> string of LEDs to give a sort of give a log(2) signal level meter....
>
> Mike
>
>
>
>
>
>>  To make up for my massive blunder, I'll offer a replacement fish for an
>>  explanation of what the following algorithm does. We'll go with the same
>>  timeframe as before, and I'll endeavor not to reply myself.
>
>>  unsigned int function(unsigned int x)
>>  {
>>   x--;
>>   x |= x>>   1;
>>   x |= x>>   2;
>>   x |= x>>   4;
>>   x |= x>>   8;
>>   x |= x>>   16;
>>   return x + 1;
>>}
>
>
>
>
> _______________________________________________
> Chchrobotics mailing list Chchrobotics at lists.linuxnut.co.nz
> http://lists.ourshack.com/mailman/listinfo/chchrobotics
> Mail Archives: http://lists.ourshack.com/pipermail/chchrobotics/
> Web site: http://kiwibots.org
> Meetings 3rd Monday each month at Tait Radio Communications, 175 Roydvale
> Ave, 6.30pm
>
> When replying, please edit your Subject line to reflect new content.
>