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.