From:	mert0407 AT sable DOT ox DOT ac DOT uk (George Foot)
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: (none)
Date:	10 Jul 1997 20:52:30 GMT
Organization:	Oxford University, England
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Chirayu Krishnappa (chirayu AT poboxes DOT com) (chirayu AT giasbga DOT vsnl DOT net DOT in) wrote:

: i need to find out if a 4 byte (default) integer has an even number of 1's
: in its binary representation or not. I need to operate on 15Mb data and do
: it fast. shifts (<<) and & is quite slow. is there some lib. function to
: do this? what is the fastest way to get it done?

I don't know how fast it would be, but I think XORing them all together
would be pretty fast:

int get_parity(int *buffer,int bufsize)
{
 int a,b,c;
 a=0;
 for (b=0;b<bufsize;b++) a^=*(buffer++);
 c=0;
 for (b=0;b<8*sizeof(int);b++) {
  c^=a&1;
  a>>=1;
 }
 return c;
}

I expect inline assembler is probably the fastest way though.

-- 
George Foot <mert0407 AT sable DOT ox DOT ac DOT uk>
Merton College, Oxford

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