Re: Re: BIT/BIT VARYING status - Mailing list pgsql-hackers

Are there any open items related to the BIT type?

> Tom Lane wrote:
> > 
> > I have made a first cut at completing integration of Adriaan Joubert's
> > BIT code into the backend.  There are a couple little things left to
> > do (for example, scalarltsel doesn't know what to do with BIT values)
> > as well as some not-so-little things:
> > 
> > 1. SQL92 mentions a bitwise position function, which we do not have.
> 
> Sorry, I have been very busy, so only got down to implementing a
> position function last night. It's a bit messy (lots of masks and
> bit-twiddling), but I feel fairly happy now that it is doing the right
> thing. I tested it with my own loadable types, as the integration into
> postgres proper stumped my somewhat. The next oid up for a bit function
> is in use already. Anyway, the patches are attached, and I'm hoping that
> some friendly sole will integrate the new position function into
> postgres proper.
>  
> > 2. We don't handle <bit string> and <hex string> literals correctly;
> > the scanner converts them into integers which seems quite at variance
> > with the spec's semantics.
> 
> This is still a problem that needs to be fixed. Also, it the parser did
> not seem to be too happy about the 'position' syntax, but I may have it
> wrong of course. I don;t know how to attach the position function to a
> piece of syntax such as (position <substr> in <field>) either, so I'm
> hoping that somebody can pick this up.
> 
> Also, i have started putting together a file for regression testing. I
> noticed that the substring syntax does not seem to work:
> 
> SELECT SUBSTRING(b FROM 2 FOR 4)
>        FROM ZPBIT_TABLE;
> 
> gives:
> 
> ERROR:  Function 'substr(bit, int4, int4)' does not exist
>         Unable to identify a function that satisfies the given argument
> types
>         You may need to add explicit typecasts
> 
> and similar for a varying bit argument.
> 
> If somebody with better knowledge of postgres could do the integration,
> please, I will finish off a regression test.
> 
> Thanks!
> 
> Adriaan

> *** src/backend/utils/adt/varbit.c.old    Sun Oct 29 11:05:11 2000
> --- src/backend/utils/adt/varbit.c    Mon Oct 30 04:58:35 2000
> ***************
> *** 1053,1060 ****
>       /* Negative shift is a shift to the left */
>       if (shft < 0)
>           PG_RETURN_DATUM(DirectFunctionCall2(bitshiftleft,
> !                                             VarBitPGetDatum(arg),
> !                                             Int32GetDatum(-shft)));
>   
>       result = (VarBit *) palloc(VARSIZE(arg));
>       VARATT_SIZEP(result) = VARSIZE(arg);
> --- 1053,1060 ----
>       /* Negative shift is a shift to the left */
>       if (shft < 0)
>           PG_RETURN_DATUM(DirectFunctionCall2(bitshiftleft,
> !                             VarBitPGetDatum(arg),
> !                             Int32GetDatum(-shft)));
>   
>       result = (VarBit *) palloc(VARSIZE(arg));
>       VARATT_SIZEP(result) = VARSIZE(arg);
> ***************
> *** 1145,1148 ****
> --- 1145,1242 ----
>       result >>= VARBITPAD(arg);
>   
>       PG_RETURN_INT32(result);
> + }
> + 
> + /* Determines the position of S1 in the bitstring S2 (1-based string).
> +  * If S1 does not appear in S2 this function returns 0.
> +  * If S1 is of length 0 this function returns 1.
> +  */
> + Datum
> + bitposition(PG_FUNCTION_ARGS)
> + {
> +     VarBit        *substr = PG_GETARG_VARBIT_P(0);
> +     VarBit        *arg = PG_GETARG_VARBIT_P(1);
> +     int            substr_length, 
> +                 arg_length,
> +                 i,
> +                 is;
> +     bits8        *s,                /* pointer into substring */
> +                 *p;                /* pointer into arg */
> +     bits8        cmp,            /* shifted substring byte to compare */ 
> +                 mask1,          /* mask for substring byte shifted right */
> +                 mask2,          /* mask for substring byte shifted left */
> +                 end_mask,       /* pad mask for last substring byte */
> +                 arg_mask;        /* pad mask for last argument byte */
> +     bool        is_match;
> + 
> +     /* Get the substring length */
> +     substr_length = VARBITLEN(substr);
> +     arg_length = VARBITLEN(arg);
> + 
> +     /* Argument has 0 length or substring longer than argument, return 0 */
> +     if (arg_length == 0 || substr_length > arg_length)
> +         PG_RETURN_INT32(0);    
> +     
> +     /* 0-length means return 1 */
> +     if (substr_length == 0)
> +         PG_RETURN_INT32(1);
> + 
> +     /* Initialise the padding masks */
> +     end_mask = BITMASK << VARBITPAD(substr);
> +     arg_mask = BITMASK << VARBITPAD(arg);
> +     for (i = 0; i < VARBITBYTES(arg) - VARBITBYTES(substr) + 1; i++) 
> +     {
> +         for (is = 0; is < BITS_PER_BYTE; is++) {
> +             is_match = true;
> +             p = VARBITS(arg) + i;
> +             mask1 = BITMASK >> is;
> +             mask2 = ~mask1;
> +             for (s = VARBITS(substr); 
> +                  is_match && s < VARBITEND(substr); s++) 
> +             {
> +                 cmp = *s >> is;
> +                 if (s == VARBITEND(substr) - 1) 
> +                 {
> +                     mask1 &= end_mask >> is;
> +                     if (p == VARBITEND(arg) - 1) {
> +                         /* Check that there is enough of arg left */
> +                         if (mask1 & ~arg_mask) {
> +                             is_match = false;
> +                             break;
> +                         }
> +                         mask1 &= arg_mask;
> +                     }
> +                 }
> +                 is_match = ((cmp ^ *p) & mask1) == 0;
> +                 if (!is_match)
> +                     break;
> +                 // Move on to the next byte
> +                 p++;
> +                 if (p == VARBITEND(arg)) {
> +                     mask2 = end_mask << (BITS_PER_BYTE - is);
> +                     is_match = mask2 == 0;
> +                     elog(NOTICE,"S. %d %d em=%2x sm=%2x r=%d",
> +                          i,is,end_mask,mask2,is_match);
> +                     break;
> +                 }
> +                 cmp = *s << (BITS_PER_BYTE - is);
> +                 if (s == VARBITEND(substr) - 1) 
> +                 {
> +                     mask2 &= end_mask << (BITS_PER_BYTE - is);
> +                     if (p == VARBITEND(arg) - 1) {
> +                         if (mask2 & ~arg_mask) {
> +                             is_match = false;
> +                             break;
> +                         }
> +                         mask2 &= arg_mask;
> +                     }
> +                 }
> +                 is_match = ((cmp ^ *p) & mask2) == 0;
> +             }
> +             /* Have we found a match */
> +             if (is_match)
> +                 PG_RETURN_INT32(i*BITS_PER_BYTE + is + 1);
> +         }
> +     }
> +     PG_RETURN_INT32(0);
>   }

> *** src/include/utils/varbit.h.old    Sun Oct 29 11:04:58 2000
> --- src/include/utils/varbit.h    Sun Oct 29 11:05:58 2000
> ***************
> *** 87,91 ****
> --- 87,92 ----
>   extern Datum bitoctetlength(PG_FUNCTION_ARGS);
>   extern Datum bitfromint4(PG_FUNCTION_ARGS);
>   extern Datum bittoint4(PG_FUNCTION_ARGS);
> + extern Datum bitposition(PG_FUNCTION_ARGS);
>   
>   #endif


--  Bruce Momjian                        |  http://candle.pha.pa.us pgman@candle.pha.pa.us               |  (610)
853-3000+  If your life is a hard drive,     |  830 Blythe Avenue +  Christ can be your backup.        |  Drexel Hill,
Pennsylvania19026