[SQL] Re: Efficiently determining the number of bits set in the contents of, a VARBIT field

I use a c function, nbits_set that will do what you need.
I've posted the code in this email.

TJ O'Donnell
http://www.gnova.com

#include "postgres.h"
#include "utils/varbit.h"

Datum nbits_set(PG_FUNCTION_ARGS);
PG_FUNCTION_INFO_V1(nbits_set);
Datum
nbits_set(PG_FUNCTION_ARGS)
{
/* how many bits are set in a bitstring? */

VarBit *a = PG_GETARG_VARBIT_P(0);
int n=0;
int i;
unsigned char *ap = VARBITS(a);
unsigned char aval;
for (i=0; i < VARBITBYTES(a); ++i) {
aval = *ap; ++ap;
if (aval == 0) continue;
if (aval & 1) ++n;
if (aval & 2) ++n;
if (aval & 4) ++n;
if (aval & 8) ++n;
if (aval & 16) ++n;
if (aval & 32) ++n;
if (aval & 64) ++n;
if (aval & 128) ++n;
}
PG_RETURN_INT32(n);
}

> Hi all,
> Am looking for a fast and efficient way to count the number of bits set
> (to 1) in a VARBIT field. I am currently using
> "LENGTH(REGEXP_REPLACE(CAST(a.somefield_bit_code AS TEXT),'0','','g'))".
>
> Allan.

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