Author: Dann Corbit
Date: 14:48:46 04/09/02
Go up one level in this thread
On April 09, 2002 at 17:32:15, Alvaro Jose Povoa Cardoso wrote:
>Does anyone kow how to do a fast 32bit bitboard mirroring?
>bit 0 -> bit 31
>bit 1 -> bit 30
>bit 2 -> bit 29
>...etc
>
>I would like to do it fast.
>
>Best regards,
>Alvaro Cardoso
From:
http://www.cs.ucsd.edu/~kgatlin/papers.html
Here is some code by Kang Su Gatlin:
int logn(int n)
{
int i = 0;
n = n -1;
while(n > 0)
{
i++;
n = n >> 1;
}
return(i);
}
int bitrev(int x, int lgn)
{
int i, t, value;
value = 0;
for(i = lgn-1; i >= 0; i--)
{
t = 1 & x;
value = (value | (t << i));
x = x >> 1;
}
return(value);
}
The logn function can be done a tiny bit faster.
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