Subj : how does this work
To   : comp.programming
From : pacman2081
Date : Sun Jul 31 2005 05:20 pm


This piece of code counts the number of one bits in integer x.

unsigned int x;

x = (x & 0x55555555) + ((x>>1)&0x55555555);
x = (x & 0x33333333) + ((x>>2)&0x33333333);
x = (x & 0x0F0F0F0F) + ((x>>4)&0x0F0F0F0F);
x = (x & 0x00FF00FF) + ((x>>8)&0x00FF00FF);
x = (x & 0x0000FFFF) + ((x>>16)&0x0000FFFF);


I have not been able to figure out how.
-- pacman

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